PU - Out. BU - Safe.
 

OK, not quite. Since it was a Major League game, it was PU - Out and U2 - Safe.

R1/R2, 1 out, top 8th, Detroit at San Francisco.

Sinking line drive to right. U1 goes out. Catch is made below the knee on the run by F9, who guns to first base.

(Insert subject line here.)

In the closest possible play requiring stop action slo-mo, R1 was out. But why would the PU even think about backfilling here when there was an R2 to start the play? U2 must've been late coming across. Leyland came out. The PU quickly yielded his call to U2. Bochy came out.

Remarkably, neither conversation got animated, and nobody got ejected. R1 was gunned down on a double steal attempt during the next batter's at bat to end the inning.

Four umpire crew, unless R3, PU would rotate over to cover 1B. U2 needs to deal with R2 (re-touch, back into 2B, etc). U3 will have R2 into 3B and the front side of a rundown.

It's very easy for the PU to come up the line to backstop U1 for R1 retouch/back into 1B & batter-runner at 1B. Ball drops - PU retreats back to HP after making any needed call at 1B.

With R1 only, sure. With R1+R2, I don't see it. Suppose R2 had the proper read on a sinking liner that fell and took off with the crack of the bat? No way the PU would get back in time if he watched the touch of the BR and positioned himself to take any throw back into first.

U2 slides over U3 slides up and the two of them cover three bases and the PU stays home.

As always, with mechanics, there's room for disagreement.

U2 needs to read this play and as soon as he sees the potential re-touch of R2 he has got to get to a mid point between 1st and 2nd to make the call at R1.

I don't like giving up the plate here, even in a ML game.