Oak/Tex PU positioning

[Hunter]

I am not an umpire, but I enjoy this forum as a lurker. My question regards umpire positioning. During yesterday's A's/Ranger's game, R1, R2, 0 outs, single to left. As R2 is approaching 3B, 3B coach is waving R2 home. As coach changes mind and puts up stop sign, PU is getting into position for possible play at 3B. PU runs between coach and 3B. If a collision between R2 and PU were to occur, is there anything? or just a train wreck? My son, who just broke his arm and may not be able to play next year, has expressed interest in becoming an umpire. He asked this question and I told him I didn't know, but that someone here would know the answer.