Just discussing last night balk call responsibility in a 4
man specifically on the leftie stepping on the correct side
of the 45 degree line in the pick to first and/or same call
for the rightie to third. In the 2 man obviously the HP
ump calls this. I feel the same way in a 4 man since he's
looking straight at the 90 degree from home to rubber whereas U1 is looking at about oh say 120 since he's up the line 6-8 feet at first on the pickoff...I can't find diddly
in the fed ump manual or in Referee's umpire guide book.
Open to discussion on this and/or reference to some written
mechanics published somewhere. THANKS!!

I bet what you would find is that it is the responsibility of ALL umpires to call balks as they see them.

Why would it matter who calls it as long as it gets called?

obviously anyone can and will call the balk. But in 4 man home and first have it the easiest.