Touching
 

A punts the ball near sideline. R25 goes out of bounds on his own and before interring back onto the field grabs the ball at the 25 yd line. What do we have?

The ball is dead when he grabbed it. If the player deliberately went out of bounds to interfere with play, illegal participation in NCAA and Fed. It's a live ball foul enforced from where B25 grabbed the ball, which is where both the foul occurred and the scrimmage kick ended.

However, R25 might only have stepped "out of bounds on his own" while legitimately running towards the ball, and that shouldn't be called illegal participation. I think you'd have to see him looking at the sideline and carefully stepping out of bounds and having to reach or step in a ways to play the ball before you'd call IP.

Regardless, let's hope R25 isn't "interring" anybody!

This is not a foul in NCAA. First, there is no such thing as illegal participation. Second, in NCAA it’s only illegal for a Team A player to return in bounds after going out during a scrimmage kick play. Because he never returned inbounds, he has not fouled. This is simply a loose ball out of bounds. It will be Team B’s ball at the B-25.

NFHS- Illegal Participation if the ball was inbounds and R25 was out.

The ball is dead, and under NCAA rules, B gets the ball, 1/10 from their own 25. Under NFHS rules, this might be illegal participation. In this case, B would have 1/10 from the 12.5 because the 15-yard penalty will be enforced half the distance.

NFHS- Illegal Participation
 

I may need some help here, but for R25 to commit illegal participation, he must return in-bounds. Since he was OOB, no penalty & ball is dead.

9-6-2 No player shall intentionally go out of bounds and b: intentionally touch the ball.