foul line

from The American Heritage® Dictionary of the English Language, 5th Edition.

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

from Wiktionary, Creative Commons Attribution/Share-Alike License.

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

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

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