Left to my discretion...or black and white?

[Steve M]

I agree with Wade - get to the field on time and handle this at the pre-game. And, for me, on time means an hour early. This approach gives me time to get lost, fix a flat, get stuck in trafic - anyne else ever get stuck behind a horse & buggy? - or even go to the wrong field. Build into your schedule time for something to happen.
Local league rules are something I don't care for - but you've got to treat them as the same as a book rule. You should have known them.
As to the other umpire letting you know you were wrong - if done away from players & teams & everyone else, OK.