I hope these two examples will remind you of the principle of Clean Hands and the proper enforcement of fouls on change of possession downs - Steve
#1) A1's pass is intercepted by Bl at B’s 40-yard line. During Bl 's return, A1 and B2 begin fighting at A's 40-yard line. Bl returns the ball to A's 2-yard line.
RULING: The head coach of B (last team in possession) may accept or decline the penalty for A's foul. If B accepts the penalty for Al 's foul, it creates a double foul so the penalties cancel and the down is replayed. B may retain possession by declining the penalty for A1's foul, in which case, it would be B's ball at its own 45-yard line following enforcement of B’s penalty (if accepted by A). Both Al and B2 will be disqualified for fighting.
COMMENT: Whenever both teams foul during a change of possession down and the team in final possession gets the ball free of a foul (with "CLEAN HANDS") they have the opportunity to retain possession. The fact that their opponent’s foul occurred after the change of possession has no bearing on the enforcement. However, when B, the "clean hands" team, retains possession by declining the opponent's foul, the penalty for B's foul may be enforced.
#2) During a legal forward pass which crosses the neutral zone, Al is illegally in motion at the snap. Bl intercepts and during his return, B2 clips A2.
RULING: The illegal motion by Al and the clipping by B2 are both live-ball fouls, but because the foul by B2 followed a change of team possession, they do not automatically constitute a double foul. The head coach of B (last team in possession) may accept or decline the penalty for A's foul. If accepted, this creates a double foul and the down is replayed. If declined, then the penalty for B’s foul is enforced if accepted by A.