Cute situation from another board

[Dakota]

I've adjusted (added detail) a bit, but I thought this was at least worth discussing from a mechanics perspective.

2 umpire crew.

R1 on 2B. R2 on 1B. B3 hits a high, long fly beyond 1B in foul territory near the fence. F9 running over to try to make the catch. R1 takes a few steps off 2B and waits. R2 runs full speed and passes R1. Batted ball drops for a foul.

OK... describe what BU does about R2 passing R1 during the live ball (before the ball becomes foul). If R2 is called out, what happens next after the ball is foul?