foul line

  1. Baseball either of the lines extending from home plate through the outside corners of first base or third base and onward to the end of the outfield
  2. Basketball a free-throw line
  3. Tennis, Bowling, etc. any of various lines bounding the playing area, outside of which the ball must not be hit, the player must not go, etc.

See foul line in American Heritage Dictionary 4

noun
  1. 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. Basketball A line 15 feet in front of each backboard from which players shoot foul shots. Also called free-throw line.
  3. Sports A boundary limiting the permissible movements of a player, as on a bowling alley or in a field event.
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