The part Bob answers is correct for both NCAA and NFHS. They are dealt with the same in both codes. The other situation like this is if the receiver steps OOB accidentally with no contact from a defender. Per HS rules, if the receiver does this, he's guilty of illegal participation the moment he steps back in bounds. If he does this while running down the sideline he technically commits the foul every time he steps out of bounds with one foot and then steps in bounds with the other foot. Enforcement is 15 yards from the previous spot and replay the down. He doesn't need to actually participate in order for the foul to occur. It's a very severe penalty. The NCAA rule is different. It only turns into a foul if the receiver is the first to touch a legal forward pass. If the ball isn't throw to him or the pass it tipped by the defense before he touches it. there is no foul. The penalty though if he is the first to touch it is a loss of down at the previous spot. It's essentially treated like an incomplete pass. The ball remains live however. If the receiver tips it, and it's caught by a defender or he catches it and subsequently fumbles and recovered by the defense, it's a turnover. The NCAA officials will drop their hat when they see the receiver go OOB to indicate he saw the receiver go OOB and knows how he got there. Any potential foul is delayed. You'll see some HS officials do the same thing, but it's not necessary. It's either a foul when he returns (went out on his own or didn't return immediately when forced out) and you throw your flag or it's not a foul (forced out and returned immediately) and no flag is thrown.