Should he stay or should he go

[bluehair]

I can’t find my Fed mechanics book and need advice on a situation that came up in last night’s game. U-16 select (but so-so teams). Pregame PU tells BU that he'll be sliding down 3BL with R1 (SOP). He'll let BU know when he’s gonna jump in on a play at 3B.

R1, no outs, runner going on the pitch with a huge running jump on F1. B shoots one in the F3/F4 gap. R1 never slowed down at 2B…long run for F9 to get the ball and PU anticipates R1 scoring attempt. Where does PU go?