<P> American football rules allow each team to have three timeouts in each half, and the NFL stops play for a two - minute warning . However, NCAA football has no two - minute warning, but the clock stops on a first down until the ball is ready for play if the play ended in the field of play . In the CFL, each team has two time - outs a game but cannot use both in the last three minutes of the game, while at lower levels of Canadian football each team has two . In Canadian football there is a three - minute rather than a two - minute warning . Also, at all levels of Canadian football, the clock is stopped after every play during the last three minutes of each half . Once the referee has set the ball the clock will restart if the last play ended with a runner tackled in the field of play . </P> <P> Timing rules change drastically after the N - minute warning in both leagues: </P> <Ul> <Li> In American football, the clock continues to run after any tackle in bounds, but stops after an incomplete pass, or a tackle out of bounds . If the clock stops, it is restarted at the snap of the ball or when the ball is ready to be played . In Canadian football, the clock stops after every play, but the starting time differs depending on the result of the previous play: After a tackle in bounds, the clock restarts when the referee whistles the ball in; after an incomplete pass or a tackle out of bounds, the clock restarts when the ball is snapped . In the NCAA the clock stops after every first down to move and set the down markers, after which the clock restarts . </Li> <Li> The penalty for allowing the play clock to run out, which is 5 yards with no loss of down before the N - minute warning in both codes, dramatically diverges after that point . In American football, the penalty for "delay of game" remains 5 yards with the down repeated . In Canadian football, the penalty for a "time count" violation ("delay of game" is a different violation in Canada) is loss of down on first or second down, and 10 yards with the down repeated on third down . Also, if the referee deems a time count violation on third down after the three - minute warning to be deliberate, he has the right to require the offensive team to legally put the ball into play within the 20 - second count, with a violation resulting in loss of possession . (Note that the enforcement of time count during convert attempts does not change at the warning; it is 5 yards with the down repeated throughout the game .) </Li> <Li> In American football, a period generally ends when time expires (though any play which is in progress when the clock reaches 0: 00 is allowed to finish); in Canadian football, the period must end with a final play . Consequently, a play is often started in Canadian football with no time (0: 00) showing on the game clock . American football typically only sees a play start with no time on the clock when a defensive penalty occurs during the last play of the period and the penalty is not declined (or, in the NFL, in the very rare circumstance when a team takes a fair catch as time expires and elects a free kick). Additionally, any period in Canadian football cannot end on a penalty (this is not the case in American football), so any penalty that occurs with 0: 00 left in Canada extends the period by at least one more play . </Li> </Ul> <Li> In American football, the clock continues to run after any tackle in bounds, but stops after an incomplete pass, or a tackle out of bounds . If the clock stops, it is restarted at the snap of the ball or when the ball is ready to be played . In Canadian football, the clock stops after every play, but the starting time differs depending on the result of the previous play: After a tackle in bounds, the clock restarts when the referee whistles the ball in; after an incomplete pass or a tackle out of bounds, the clock restarts when the ball is snapped . In the NCAA the clock stops after every first down to move and set the down markers, after which the clock restarts . </Li>

Size of rugby ball compared to american football