American Football NCAA Rule 3-3-9-b

b. When the helmet coming off is the only reason for stopping the clock, other than due to an injury to the player or their teammate (Rule 3-3-5), the following conditions apply (A.R. 3-3-9-I-III):
1. The play clock will be set at 25 seconds if the player is on offense and at 40 seconds if the player is on defense. With one minute or more remaining in either half, the game clock will start on the referee’s signal.
2. Ten-Second Runoff. If there is less than one minute in the half the opponent has the option of a 10-second runoff, unless the helmet comes off as the direct result of a foul by the opponent.
3. If there is a 10-second runoff the game clock will start on the referee’s signal. If there is no 10-second runoff the game clock will start on the snap.
4. The 10-second runoff may be avoided by the use of a charged team timeout, if available.
5. There is no option for a 10-second runoff if helmets come off opposing players. (A.R. 3-3-9-V)