Calhoun,
I believe your question, for NCAA, is regarding a foul ONLY by team A, following a change of team possession during a try. The penalty is declined by rule, unless it is a flagrant foul (requiring ejection), and the try ends. If the foul is flagrant, the penalty is enforced on the succeeding kickoff/at the succeeding spot in an extra period.
If BOTH teams foul AFTER the change of possession, those fouls cancel, any score is canceled, and the try ends. If one of the fouls was flagrant, it would be enforced on the succeeding kickoff/at the succeeding spot in an extra period, and the player would be ejected.