I am interested to see what the experts here have to say. But I know from my training is let the ball take you to the call. Yes by the book you release that runner to PU but you also have the back side of a run down, so I would say you have to try and do it all, that is why we get paid the big bucks
. But seriously I would have my head on a swivel and attempt to watch BR and R2 but once I see the ball coming in and the imminant play at 3rd that is where my attention is going to be, R2 and BR can't be doing anything since R1 is hung up at 3rd so not much to watch(OBS possibly but there is no chance to advance) so let the ball take you to the play and the play is at 3rd. Again not sure if this is a rundown, but if it is I am pretty sure the call coming back into 3rd would be your call! Again interesting to see what others have to say.