[tcannizzo]

From what little I know:

F5 was straddling 3B.

The runner slid into her left foot before F5 recieved the ball at which point U1 in B extended left arm for DDB/OBS, waiting to see how the play developed.

F5 dropped the tag down on R1's foot which was still blocked by F5's foot.
U3 who was positioned about 2-3 feet off the foul line, called R1 OUT.

U1 then began approaching the play, still with left arm extended but saw F5 throw across the diamond on a play on BR. Upon seeing this U1, hollered DEAD BALL - DEAD BALL to kill the subsequent play since the delay was now off.

With the throw coming from F2 only a few feet up the 3B line, U3 may not have been in the best position to determine whether the ball was already in the glove of F5 when R1 slid into F5's foot.

Defensive coach asked U1 about the call.
Coach: "But Blue, F5 was about to recieve the ball."
U1: "Exactly the same thing I saw coach, that is why Obstruction is the correct call."
Coach: started to say something else but was interrupted when both PU and U3 approached the meeting.

PU told U1 that it was U3's call.
U1 was stupified to be confronted by 2 other umpires, interrupting meeting with single coach, but asked, "Why are you out here to give me help, when I didn't request it?"
PU said, "I can't let you take the call away from U3."
U1 said, "We are not having this conversation." And walked back towards B.
Just at that point, PU was near the circle on the way back to HP, and then signalled OUT.

U1 walked off the field at that point.

U1 is probably blacklisted from here to eternity by now.