what happened here?

[KJUmp]

Originally Posted by MD Longhorn

Honestly ... didn't see U3 chase on first watch. And he did that kind of halfway, which likely caused PU's confusion and U1's rotation. If you're going out, GO OUT! Looks like he sort of rotated, sort of chased, and got caught in between.

He did go out. He Paused, Read the play, and Reacted by chasing.
At 0:20 batter has made contact with the pitch.
At 0:22 U3 has pivoted w/back to infield and chasing into OF toward centerfield, then peels of to his right when he sees there's no catch.

U3 and U1 (in covering for PU) did their job. I'll say again, this rotation getting off the rails was the fault of the PU.
PU didn't read U3's chase and moved straight down the 3rd base line rather than initially moving to the holding area in front of the circle; and judging by what we see in the video, my guess is that he failed to communicate to U1 that the crew was now in two-man coverage.