foul line

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Baseball Either of two straight lines extending from the rear of home plate to the outer edge of the playing field and indicating the area in which a fair ball can be hit.
2. n. Basketball A line 15 feet in front of each backboard from which players shoot foul shots. Also called free-throw line.
3. n. Sports A boundary limiting the permissible movements of a player, as on a bowling alley or in a field event.

Wiktionary

1. n. basketball A line from which a player takes a free throw
2. n. baseball, softball One of the two lines on the edge of a field marking the area inside which a fair ball may be hit.
3. n. bowling A line between the lane and the approach, which the bowler must not cross.

WordNet 3.0

1. n. a line across a bowling alley that a bowler must not cross
2. n. lines through 1st and 3rd base indicating the boundaries of a baseball field
3. n. a line from which basketball players take penalty shots