In addition to the situations already mentioned above as plate appearance
s that do not count as at-bats
s, sacrifice flies, sacrifice bunt
, and hit by pitch), both obstruction
and catcher's interference
also are not considered at-bats.
Batting average is usually presented out to 3 decimal places (as mentioned above), because that's usually sufficient (similar to as pi is usually written as 3.14). However, the actual batting average can be written out to more decimal places (as with pi or any other calculation). For example, in 1984, Dave Winfield and Don Mattingly battled all season for the American League batting lead. Towards the end of the season, newspapers would show their batting averages at that date, usually out to 4 digits instead of 3 ("Mattingly .3403, Winfield .3397", for example, rather than both at .340)
Batting .400 has been one of the several historic baseball landmarks that is often chased, but not achieved. The last time someone hit .400 in a season was Ted Williams in 1941 (he hit .406). Since then, there have been some close calls (Tony Gwynn hit .394 in the strike-shortened 1994 season; George Brett batted .390 in 1980). See also .400 batting average.
Batting .300 has often been a sign of an All-Star caliber player. However, in 1968, Carl Yastrzemski led the American League with a mere .301 batting average, the lowest average ever to lead a league (several conditions led to the drop in batting average that year).
For info on batting .200, see the Mendoza line.
The all-time career leader in batting average is Ty Cobb with a .3664 average. The single-season record is .4850 in 1887 by Tip O'Neill (not the former speaker of the house, by the same name). In the 20th century, Nap Lajoie batted .4265 in 1901 and Rogers Hornsby hit .4235 in 1924.
Batting average is usually abbreviated as AVG (and sometimes BA).