[greymule]

Disagree. I've seen this play more than once. F5 doesn't have to run R2 back very far—just enough. If R2 is about halfway to 3B when F5 throws to F4, there should be time to get R2. Obviously, the throws have to be quick, so you don't see the play at levels where F6 is still cutting off F2's throws to 2B with a runner on 3B.

It's the same as R1, ground ball to F4, who attempts to tag R1. (We've all seen plays in which F4 attempts to tag R1 rather than throw to F6 at 2B.) R1 backs up to delay the tag. The play is to throw to 1B to get the BR and then play on R1.

Obviously, if R2 has progressed far enough toward 3B, the play isn't going to be possible. It requires a ground ball to F5's left, with the "confrontation" with R2 occurring quickly.