The phrase "foul line" refers to a line on a sports field or court that marks the boundary between fair play and foul play. If a player or ball crosses this line during the game, it is considered a violation or foul. Full definition
One year, he made only three out of every 10 shots, and last season, when he managed to sink two free throws in a row during post-season play - offs, he made headlines («Chris No Dud at Foul Line!» (discovermagazine.com)
Well, nothing except the ball hitting the yellow stripe on the left field foul line in a very ambiguous spot. (sbnation.com)
He also grabbed an impressive popup along the third base foul line in the fifth, so he's had a busy day. (sbnation.com)