Asking for Help

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2 man crew in a game I watched tonight.

R1

RHP picks off R1 but the base umpire calls him safe because he can't see that the runner's hand is not on the base. F3 dropped straight down with the knee and prevented the runner from touching the base.

I could see it because I was looking straight down the first base line so I assume the HP umpire could as well.

I completely understand how the field up didn't see it.

However, what would prevent that umpire from asking the home plate ump if the runner touched the base?