Confusion on Friday night
 

Play/penalty that happened in a rivalry game on Friday night confused me. I'd like to give the officials the benefit of the doubt, but I can't think of what may have been called that fits all the pieces of the puzzle here.

1st and 10 on A9. Sweep is run to the home field side for approximately 9 yards. During the run (definitely during the play, not after), the H throws a flag towards the LT/DE on his end of the line of scrimmage (the opposite side of the direction of the run).

When the play is over, R signals a dead ball personal foul on Team A. They place the ball back on the 9 yard line (they do not march off any penalty yards), 2nd and 10.

My best guess is this was a USC foul with an incorrect signal.

From the enforcement it sounds like everything "during" the play was legal. So, it must have been either a dead ball Personal Foul or and USC (both of which are enforced from the succeeding spot and the down would count.) If it was in fact a dead ball foul (either PF or UNS) then they got it correct, enforcing back half the distance to A's 9 and counting the down.
Had it been a live ball PF the down would have been repeated and penalty enforced from the spot of the foul if it was behind the end of the run.

Also, if first down yardage is gained on such a play (with a dead ball foul penalty), then after penalty enforcement against A, it is first and 10 (even if the ball ends up, due to the penalty, behind the original first down mark)

Half the distance enforcement on that gain would put it back where the series began. As mentioned, a DBF, the down counted.