A bowling foul is called when any part of a bowler's body — foot, hand, clothing — touches or crosses the foul line during a delivery. The foul line is the thin black line (or electronic sensor line) at the beginning of the lane surface, 60 feet from the headpin. In sanctioned competition, fouling has specific consequences that can significantly affect your score.
What Constitutes a Foul
Under USBC rules, a foul is committed if any part of the bowler's body touches or crosses the foul line, or any part of the lane, equipment, or building beyond the foul line, during or after a delivery — before all pins have come to rest. This includes:
Your sliding foot crossing the foul line as you release the ball. Any part of your body touching the lane surface past the foul line. Your ball passing through a gutter (beyond the foul line marker) if your hand follows through over the line. Falling forward and catching yourself past the foul line after releasing the ball.
It does not include: your ball briefly touching the foul line indicator before it crosses onto the lane. Releasing the ball correctly and then stepping over the line after the ball has left your hand — though USBC rules technically include "after" the delivery, the standard interpretation is during the delivery.
Consequences of a Foul
On the first ball of a frame: The delivery counts as a zero — even if you knocked all 10 pins down with a technically perfect strike. The pins are respotted, and you bowl the second ball with all 10 pins standing. You cannot score a strike in a frame where you fouled the first ball.
On the second ball of a frame: The delivery counts as zero. Any pins knocked down do not count. If all 10 pins had been knocked down on the first ball (a spare), the pins are respotted — but since you're on the second ball, only the remaining pins from the first delivery matter. A zero is recorded for that ball.
In the 10th frame: Fouls in the 10th frame follow the same zero-ball rule. If you foul on the first ball of the 10th frame, the ball counts as zero, all pins are respotted, and you bowl your second ball with all 10 standing. Foul on your bonus ball in the 10th (after a strike or spare), and it counts as zero.
Why Fouls Happen
The most common cause of fouls is a slide that goes too far — the bowler's momentum carries their foot past the foul line as they complete their approach. This is especially common when bowlers speed up their approach under pressure, change their footwork mid-game, or are wearing shoes with excessive slide soles for the approach surface.
Occasionally, fouls result from misjudging starting position — if you start too close to the foul line, even a normal slide crosses it. Always set your starting position with room to slide: most bowlers slide 6–12 inches, so starting with your toe 12–18 inches behind the foul line provides margin.
In Casual vs. Sanctioned Play
In casual recreational bowling, fouls are almost never called unless they're blatant — the competitive penalty structure doesn't apply when you're bowling for fun on a Friday night. In league and sanctioned tournament play, fouls are enforced and scored as described above. At major tournaments, additional officials monitor the foul line and fouls can be protested if they're not called but observed.