American Football Rules IFAF Approved Ruling 3-3-9 :I-III

I. After the ball is dead, A55 blocks B33 at his waist, knocking him to the ground. As B33 hits the ground his helmet comes off. RULING: Dead-ball foul by A55, 15-yard penalty from the succeeding spot. B33 must leave the game for the next down as his helmet came off
through play and not due to a helmet foul. B33 may remain in the game if Team B takes a timeout. [Cited by 3-3-9-b]
II. Late in the first quarter ball carrier A22 is legally tackled, and his helmet comes off just after his back hits the ground. The game clock reads 0:00. RULING: A22 must leave the game for
the next down, which will be the initial down of the second quarter. A22’s helmet came off through play and there was no helmet foul by Team B. However, A22 may remain in the game if Team A takes a timeout. [Cited by 3-3-9-b]
III. During the down A22’s helmet comes off (no helmet foul by the defense) and B77 goes down with an injury. The ball carrier is tackled inbounds. When the clock is stopped it reads
0:58 in the fourth quarter. RULING: Unless Team A takes a charged timeout, A22 must leave the game for one play. The play clock is set at 40 seconds, due to the defensive injury, rather than 25 seconds due to the helmet coming off the offensive player. There is no option for a 10-second runoff because the clock stops for both the helmet off and the injury, and these occur for opposing players. [Cited by 3-3-9-b]