Lacrosse is played on a field that is 120 yards long by between 53.5 and 60 yards wide.

There is are two 6'x6' square goals that ars six feet deep and terminate in a triangle. The goals are surrounded by an eighteen foot diameter circle known as a "crease." A goal sits ten yards from the end-line at each end of the field.

The field is divided by three lines: the midfield line, and two restraining lines that sit halfway between the midfield line and the end line.

Every player on the field except the goaltender must wear a helmet, protective gloves, shoulder pads, and elbow pads. Most players will wear padded rib guards as well. Goaltenders are usually somewhat unhinged (trust me, I am one), and are only required to wear a helmet, gloves, a throat guard, and a chest protector. There are some goaltenders out there who have not been touched by the hand of the goaltending god who will wear shoulder pads, elbow pads, thigh pads, and shin pads in addition to the required protection. Oh yeah, you'll also want to wear a cup.

Every player on the field has a lacrosse stick. The dimensions and "feel" of the stick depend on the position the person plays. Sticks are made of aluminum, carbon fiber, titanium, or my favorite for wholesome bone-crushing goodness, wood.
Midfielders and attackers use a stick that is no less than thirty inches long and cannot have a pocket deeper than the diameter of one lacrosse ball. The stick should be short to prevent someone from beating on the butt of the stick.
Defensivemen have a stick that is reminiscent of an old English quarterstaff. It should come at least to your chin and be even with your head if possible. The extra length is useful for spearing a wayward attacker with poke checks or delivering a spleen-jarring slap check.
The goaltender has a stick that looks like a cross between a bushel basket and a fishing net. It has a gigantic head and has a shaft that is normally between 25 and 44 inches long. I liked to keep mine on the longer side for the extra leverage, but some goaltenders think that a shorter stick makes them more agile.

Each team has ten players: three attackers, three midfielders, three defensivemen, and one goaltender. Attackers stay near the opposing goal and try to score. Midfielders are masochists who constantly run the length of the field trying to dominate the ball. Defensivemen keep the ball out of attacker's hands. Goaltenders (hopefully) keep the ball out of the goal and act as general for the defense.

After each score and at the beginning of each half play begins with a face off. This is done by placing the ball on the ground between the sticks of two kneeling midfielders. The referee blows the whistle and both teams unleash Hell. A point is scored by placing the ball into the opposing goal.

There are many penalties in lacrosse. Penalties are releasable or non-releasable. If a penalty is non-releasable the player does not return to the game after a goal is scored. Here are the basics:

Slash: You hit someone in the head with your stick. You get thrown in the penalty box for one minute.
Cross-check: You hold your stick like a quarterstaff and push someone with it. You get thrown in the penalty box for one minute.
Tripping: You trip someone. You get thrown in the penalty box for one minute.
Spearing: You use your head as a battering ram. You get thrown in the penalty box for one to three minutes.
Personal Foul: This is the catch-all term for doing something stupid like breaking your wooden stick in half and attempting to stab somebody with it. This will get you one to three minutes in the penalty box.

Offsides: There must be no less than four players on the defensive side of a team's field at a time. If a team violates this rule the other team gets the ball at midfield. This cannot be violated if a man is in the penalty box.
Offensive Crease Infraction: An offensive player may not enter the crease. Violaion results in a free clear.
Defensive Crease Infraction: A defensive player may not enter the crease with the ball. A goaltender may not re-enter the crease with the ball. Violation results in a loss of possession.
Moving Pick: An offensive player may not move and impede the progress of a defensive player. Violation results in loss of possession. Equipment Infraction: A player must wear all protective gear and meet the design requirements for a stick. Violation is a three minute penalty, non-releasable.

If people seem to be looking at this node I will add some strategy and tactics.