Fair Catch Fiasco

[parepat]

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K is down by three with less than a minute to go. K attempts an onside(s) kick from its 40 yard line. K1 kicks the ball into the ground and the ball then bounds high into the air. R1 gives a proper fair catch signal at the fifty yard line and completes the catch. As soon as R1 catches the ball he is hit by K2 and fumbles. K3 Recovers at R's 45.

Questions.
1. What is the foul?
2. When does the play end?
3. What are the enforcement options?
4. Whose ball?

This play actually happened to us this year.