Taken from the original at http://www.ecst.csuchico.edu/~beej/guide/net/ ... see end of writeup for Copyright statement.


Blocking. You've heard about it -- now what the hell is it? In a nutshell, "block" is techie jargon for "sleep". You probably noticed that when you run listener, above, it just sits there until a packet arrives. What happened is that it called recvfrom(), there was no data, and so recvfrom() is said to "block" (that is, sleep there) until some data arrives.

Lots of functions block. accept() blocks. All the recv*() functions block. The reason they can do this is because they're allowed to. When you first create the socket descriptor with socket(), the kernel sets it to blocking. If you don't want a socket to be blocking, you have to make a call to fcntl():

#include <unistd.h>
#include <fcntl.h>
sockfd = socket(AF_INET, SOCK_STREAM, 0);
fcntl(sockfd, F_SETFL, O_NONBLOCK);

By setting a socket to non-blocking, you can effectively "poll" the socket for information. If you try to read from a non-blocking socket and there's no data there, it's not allowed to block -- it will return -1 and errno will be set to EWOULDBLOCK.

Generally speaking, however, this type of polling is a bad idea. If you put your program in a busy-wait looking for data on the socket, you'll suck up CPU time like it was going out of style. A more elegant solution for checking to see if there's data waiting to be read comes in the following section on select().

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Copyright © 1995, 1996 by Brian "Beej" Hall. This guide may be reprinted in any medium provided that its content is not altered, it is presented in its entirety, and this copyright notice remains intact. Contact beej@ecst.csuchico.edu for more information.


  • Part of the rehearsal process of a play where the moves to be made by the actors during the play are communicated to them. The stage manager will record these for future reference.
  • The work (by a director) of visualizing and creating these moves.
  • The movement around, across, and on stage an actor makes during a play while acting.
  • Improvisation: obstructing the narrative of the scene, by refusing the offers of your partners.

Knitting (also applies to crochet):

Blocking is one of the final steps in creating a garment, to give one's knitting an even, professional finish, smoothing out minor imperfections and adjusting the final shape to the desired dimensions. Flat knitting is blocked prior to seaming to avoid inadvertent biasing when garment pieces are sewn.

There are two basic steps to blocking: dampening and shaping. The item is dampened, shaped and allowed to dry completely. Dampening can be done either with cool water or with steam.

Although blocking smoothes out minor imperfections, it cannot work miracles with a poorly knitted item. Garments can be blocked a little larger, wider and shorter, or narrower and longer; they really cannot be blocked smaller.

In gamer-speak, any action that prevents the free movement of another player is referred to as "blocking." More specifically, standing still in narrow corridors, on stairs, or near corners will invoke the wrath of your teammates and angry imperatives to "quit blocking, noob."

In order for blocking to take place, a few things must happen. First, the game must have some form of player-model collision. If players can walk through each other, then the only blocking that will be going on is visual. Second, blocking usually occurs in team games. In a lone wolf deathmatch-type game, blocking is much less likely to occur, as players have every reason to shoot the offender rather than try to navigate around them.

Blocking can occur for several reasons. One of the more common is the fact that many people simply don't think in a team-oriented fashion, and don't realize that when they stop in the middle of a hallway to return fire, they're preventing their teammates from reaching much-needed cover.
Another common reason is that the player who is blocking is doing so on purpose, either because he's an all-around jerk, or because he has tired of playing on this particular server and has decided to make life difficult for his teammates before he parts.

Whatever form it takes, blocking is an unfortunate occurance that has irritated many players since gaming's inception, all the more frustrating because of the fact that there isn't much anyone can do about it, aside from team-killing, which is frowned on as much as or more than blocking.

This writeup focusses on blocking for crown molding. The term 'blocking' is a general carpentry term and, as such, may at times apply to load bearing applications.

The interior wooden framework built to support crown molding. It may be used on top of cabinetry, at the join of wall and ceiling, in mantel and valance buildups, and in other applications.

Blocking is usually necessary with stacked crown molding, and always necessary when applying even a single layer of crown molding to frameless cabinets or full overlay framed cabinets if the molding in question does not have a flat bottom side by which it can be attached.

The size and shape of the blocking necessary depends on the intricacy of the crown and on the skill of the installer; it might be a small 1" x 1" (2.54cm x 2.54cm) rail, an elaborate infrastructure made of several pieces, or anything in between. It does not have to be pretty because you'll never see it. Typically, blocking for moldings bears no loads other than the weight of the moldings.

Some finish carpenters include the cost of blocking in their basic price for crown installation. Others may charge extra to account for the additional time required and the cost of the material used for the blocking.

Side view of the top of a wall cabinet, showing the cabinet box, door, crown molding and blocking in cross section

∏ - blocking
c - body of the cabinet
d - cabinet door

     |/   \
    /ξ     | ← crown
  ∏|/     /

Skill and experience are required to install crown as shown above. Even small errors can result in gaps between the crown and the top of the cabinet through which light can be seen. These gaps can be wildly obvious, especially if you are backlighting the crown onto the ceiling. I've had a few contractors tell me they take out some extra insurance by applying color matched caulk on the inside of the framework.

A two piece stacked crown molding is easier in some ways:

     |/   \
    /ξ     | ← crown
  ∏|/     /
 ===ℑ    /

Here, the '===ℑ' represents a second piece of molding which is flat and has a decorative front edge. The crown, the blocking, and the flat piece are attached together squarely and then mitered as a whole. It is easier to attach the crown stack to the top of the cabinet due to the flat piece, and since the flat piece is... flat, there is far less chance of gaposis.

This is only the most general overview of blocking for crown molding. If you are not extremely comfortable working with crown molding and using a compound miter saw, I strongly urge you to hire a finish carpenter. If you want to try it yourself, practice first! Solid wood crown molding can cost from $50 to way over $500 US per 8 foot (~2.5 m) length, and once you start stacking it, the price shoots up from there. There is always waste when cutting crown, but at those prices, you will want to minimize it. For practice, buy several long pieces of the cheapest plastic molding you can find – more like $20-$30 apiece – and be prepared to waste it all.

I've had several people tell me that installing complicated crown molding is an art, not a science. One person once said to me, "I could tell you exactly what to do, and you'd still screw it up." I rely on my contractors to tell me whether the crown systems I devise will work as I expect, and I rely on their craftsmanship to ensure that the installation goes smoothly and the result is beautiful.

Actions used by offensive linemen in American football to move defenders away from the play of the ball. Blocking means pushing someone in the direction you want him to go, or to prevent a defender from getting to an area of the field you and your teammates are guarding. I shall assume you know something of the rudiments of the game.

The Offensive Line

The offensive line is defined as the five players who block and who are not allowed to catch a forward pass. They consist of one center, who snaps the ball to start the play, two guards, and two tackles.

At the beginning of a play, the offensive team lines up about the ball. The center holds the football, which still touches the ground, and prepares to snap it to the quarterback to begin the play. Immediately to his left and right are two guards. To their outside are the two tackles.

The blocking assignments are
C - Center
G - Guard
T - Tackle

A center is at the center of the offensive line. He must block straight ahead or left or right. Usually the defensive line will have only four men, and he does not have a DL assigned to him. He will help out to block whichever guard will need the most help. Sometims he will run downfield and block a linebacker, a difficult assignment. As head of the corps of offensive linemen, he is their anchor and their brains. He will have to adjust his linemen's blocking assignments if he feels the defense is going to do anything tricky. A good center in professional football will be about 6'4" and will have wrestled as a heavyweight wrestler. His lateral movements are very good.

A tackle is large and in charge. He is an anchor blocker, which means he is one of the largest and strongest men on the team. When a pocket of blockers collapses around the quarterback during a passing play, a guard and a tight end will block next to him in a formation reminiscent of a Greek phalanx: shoulder to shoulder. A tackle is a quiet man, but brutally strong. He takes it as a point of honor that none shall pass him. Professional tackles are behemoths. They can be 6'6" or bigger and usually weigh north of 300 lb. They are surprisingly agile for such big men. Watching an offensive tackle and a defensive tackle (also a large man) crash into each other is like watching two sumo wrestlers collide.

A guard is what's left over: He's about the same size as the center but less coordinated. He has good straight-ahead strength. He fits well with the rest of the line. He's dependable. Pulling guards are rarer than hens' teeth, because they have to be big AND run fast.

Basic Blocks

Blocking techniques are well described, with diagrams, at http://eteamz.active.com/football/instruction/tips/tip.cfm/589/

"There are three Golden Rules of Blocking. First, the blocker must keep his head between the defender and the play, maintaining proper position. Second, the feet never stop moving. And third, blocks are maintained until the whistle", which signals the end of the play.

There are ten basic types of block an offensive lineman uses. I shall describe some of them here.

The drive block is the most basic: the lineman fires out of his stance into the chest of the defensive lineman, low and hard. Feet keep churning. The objective is to move the lineman from his position. It's a strength on strength move. This is usually called for when the ball is being run into this area.

The read block calls for the blocker to make contact with the defender in the middle of the torso and "read" the defender. The idea is the defender will choose a shoulder to attempt to go around, and the blocker then proceeds to assist the defender in that direction. This is used when the direction of play is away from the OL's area of play, and it doesn't matter where the DL is getting moved to. It's a half-strength move that uses leverage against the defender.

The position block has the blocker position himself between the play and the defender. I can't describe this any better than the author does: "If the defender to be blocked is already lined up in such a manner, this block might be referred to as an Angle Block. If the defender has the superior angle on the blocker, then the blocker will attempt to "Hook" the defender. This is accomplished by making contact with and sliding the head to the outside of the defender. The blocker turns his behind to the running lane fully placing himself between the defender and the play. The hands are extended."

The double team block is when two blockers block the same man. A defensive back like a linebacker who rushes to fill the exposed gap is usually met by another blocker: either a pulling OL or a fullback. The collision of these two giants, who are running at full speed at each other, is something to behold. Linemen are taught to watch their knees for rolling bodies during the play.

The trap block is a bit of trickery which counts on a defensive lineman's over-aggressiveness. The blocker purposely vacates his spot, which permits the DL to rush in unopposed. He's counting on being hit, but when he's not, he's leaning into the run, and for a split second is off balance. Another lineman further down the line blindsides him with a block. The clipping penalty is not in force when blocks happen in the region between tackles, which permits this blocking to be legal. The block, if done correctly, is an enormous surprise to a DL and can be effective if used infrequently, but it requires a great deal of training to get the timing and coordination right. Trap blocks are practiced over and over again in blocking practices, but are only used a few times a game. Sometimes this is called a crack-back block, or simply a crack-back.

The cross block attempts to take advantage of pre existing angles at the point of attack. Which blocker "goes first" is determined by the running lane and defensive alignments and tendencies. Good communication between the offensive linemen is a must in order to properly execute a good cross block.

The cross pull block has the pulling blocker coming from his own side of the line across the Center position to the other side. The Pull Block occurs when the pulling player pulls to the same side of the line he is on, going even wider toward the side line.

Other blocks are mentioned at the web site mentioned above, but it's hard to explain them without actually playing the game.


An offensive lineman is not permitted to grab and hold the uniform of a defensive player. He must keeps his hands open or tucked close to his uniform. Blocking point of contact is at the offensive lineman's helmet and shoulder pads. If a defender must be driven right, the offensive lineman sticks his helmet to the left of the defender, and vice versa. Blocking is hardest on the legs and knees. Blockers are prone to knee and back injuries, since these joints absorb most of the impact of a large lineman.


Training consists of a strength and conditioning regimen as well as skill drills.

Conditioning consists of weight training: bench presses and leg presses, as well as the usual arm and Pilates-like core conditiong exercises every athlete must endure. Runs develop the cardiovascular system.

Blocking sleds are the bane of every OL's life. They are man-sized pads attached to a flat metal boat-like structure that can slide across grass. You line up across from a dummy, and when the coach calls a whistle, you fire out of your stance and hit it, full speed. The boat moves a little. When you pop the sled, you drop to the ground, roll over like a dog, and get back into a stance ready to hit the next dummy. There are eight dummies per sled. Sometimes the offensive line coach, who's standing on the sled, wishes the sled to be moved across the field. This is when you start wondering when exactly you're going to puke. Because you will, eventually. Imagine doing blocking drills under the hot Alabama sun, under the merciless stare of Paul "Bear" Bryant, The University of Alabama's tyrant for so many decades. Only a few players died under his tutelage. This thought consoles you.

Skill drills are where blockers learn the choreography of the blocking patterns. Direct blocks are practiced with a man directly over you as well as when the defensive linemen line up in the gaps beween you and your teammate. Trap blocks and pull blocks are practiced over and over and over again until you can do them in your sleep. Containment blocks, used during passes, can't be taught except with live, rushing defensive linemen seeking to destroy your quarterback. You learn how to collapse your pocket of protection, and you learn how to adjust when your QB scrambles out of the pocket.

Social aspects

Linemen are likely to socialize more than any of their teammates. Since their blocking assignments are so highly choreographed, they want to get to know each other both on and off the field. They have dinners together and party together. It is something to see four or five big uglies dancing at the same time. For some reason they seem to marry the most petite women imaginable.

Want to know why Green Bay Packers quarterback legend Brett Favre is so popular with his linemen? He does blocking drills with them (or at least he used to). He has a workmanlike attitude they find endearing. He's not a prima donna. He takes hits like a man, and he doesn't complain about injuries. They don't comment when he's hurt, but they notice. If there's something a lineman knows, it's playing with pain and injury.

"He has played through a torn knee ligament and a broken thumb and despite that has started 209 consecutive regular season and playoff games. While other quarterbacks are often held out for lesser injuries, Favre continued to play through them and play through them at a high level." - Devastakar

He praises them in interviews. Nothing a lineman likes better than being praised by your quarterback. You may be quiet and shun the limelight, but it's still nice getting an attaboy from the star of your team. And he buys dinners for them. Praise is nice, but ribs is nicer, yassuh. Pass the sauce, would you, Brett?

"That Favre would celebrate primarily with his linemen, the big uglies, made him more of a champion for the unheralded." - Devastakar

Color commentator Terry Bradshaw was a Pittsburgh Steelers quarterback who also endeared himself to his linemen. He was almost as big and almost as strong as some of his linemen, and had the joie de vivre they enjoyed. He hung out with his linemen and partied with them. They loved him for it.

The interior game

I've written about blocking in technical terms, but now I wish to describe to you what it's like to actually block as an offensive lineman. I played football at a variety of skill positions at the high school football level, including playing offensive guard when I was needed there.

Defensive linemen are big and fast. They come off the ball fast, straight ahead. They wish to knock me down and run over me in pursuit of the man with the ball.

The stupid ones rarely look at the offensive lineman - he's merely an impediment. They think their strength will win the duel. If he's weak, I can handle him myself. Since I know the snap count, I try to get lower than him, below his arms, and raise him up with a forearm shiver before he has time to react. If I can get at his hip level and drive his body up, I have won. A man cannot rush effectively if his body isn't parallel to the ground. If I am much stronger than he is, it would give me great joy to knock him on his ass. There is no greater happiness standing over a man, while your arms are taped up and padded and look down on him with a glower and a promise to do it again the next time.

If he's strong, my fellow center or tackle will assist with the blocking.

A smart defensive lineman is incredibly hard to block. He doesn't have to be strong, just smart and quick. He will look at me to attempt to read my blocking stance. Will I block him left, or right? Will I even block him at all? Perhaps I will block the man on his left or right, and let someone else block him. He will look at my eyes to see where I am looking, but he will also look at my fingers: are they held normally? Are they clenched in abnormally tight clench? Do I look nervous? This usually tells him the run is right through my hole, and that I'm nervous about this next play.

When I line up in my stance, I can't give him any reads or, as poker players call them, tells. On passing plays, I have a tendency to rock back on my heels, because I will be retreating into a pocket around the quarterback. On block plays, I tend to lean forward and breathe harder for the blow-out block. But against a smart player I can't show anything that will give him an indication of the play's direction.

As we line up for snap count, the defensive linemen are talking to us. "You cunt. I'm going to hit you so hard your mamma's gonna have to call an ambulance." I shouldn't be saying anything, because I'm listening to the snap count or to check off colors, when my quarterback changes the play at the line of scrimmage. However, I'm looking at my man as well. Is he going to go to my left, to my right, or just bullrush me right up my numbers? I am also summoning my energies to hit him. I don't want to just hit him, I want to control the motherfucker. I want to dominate him. I want to humiliate him. And the guys on either side of me are looking up at their men, thinking the same thing.

The center may take his free hand and point, and tell us how we're to block. He is free to do so until we get into our blocking stance. From then on, we are not permitted to move until the ball goes into play.

The ball is snapped. Mayhem ensues. How to describe this part? Well, it's about three seconds of pure violence. I fire out of my stance, like a runner out of sprinting blocks, feet wide apart, churning and moving all the time. My arms come up to hit him hard. He's doing the same to me, but he has the luxury of using his hands to grab my jersey and pull or push as he wishes. I know where my runner is moving, so I block to give my runner a nice hole to run through. Feet moving. arms furiously hitting my man as furiously as he's hitting me. One of us crumples first. Sometimes we collapse to the ground in a big pile, both exhausted.

In the pile of bodies that is the trench, there's a lot of pushing and shoving. Sometimes biting. MOTHERFUCKER WHO BIT ME? Sometimes a finger into the eyes. This is when fights start. We understand dirty trench fighting, but this is not permitted by unspoken convention. Fingers get twisted. My back gets stepped on by somebody. Whistles are blowing, signalling the end of the play, but my face is down in the mud. I can't see a damned thing until everybody else gets off me. My man pushes off me one more time. "Beat you that time cocksucker." I look up. I'll put my helmet against his and smile and say, "We made fifteen fucking yards, stupid. Eat shit and die." His eyes will flash and he'll say, "I'm going to fucking destroy you." "Any time, any where, bro."

Ladies and gentlemen, that's blocking.


  • http://eteamz.active.com/football/instruction/tips/tip.cfm/589/
  • http://eteamz.active.com/football/instruction/tips/tip.cfm/1669/
  • http://www.devaskarsports.com/national_football_league/brettfavre0904.html
  • JohnnyGoodyear's encyclopedic knowledge of American football. Love ya, guy. :-)

Kind words

well done on your Blocking w/u. As a college offensive lineman, you have impressed me. Do note that all positions on offense can and do block, as well as defensive players during a turnover. You might want to mention something about crack blocks with wide receivers on defensive backs. Also important are cut blocks. And it might seem mundane to you, but I would replace "leg presses" with squats for a variety of reasons. Basically all olympic lifts are good for football players, but especially linemen. Also, you are dead on with the social aspects. It might be worthy to note that OL tend to be the funniest, goofiest and smartest guys on the team. Again, very nice w/u.
-- Tonic

Block"ing, n.


The act of obstructing, supporting, shaping, or stamping with a block or blocks.


Blocks used to support (a building, etc.) temporarily.


© Webster 1913.

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