You have to nip it in the bud early and without delay. If one team starts jawing at you, pull their coach or captain aside and tell him to get his team under control or you'll start sending players home early.
There is no reason to accept disparaging remarks from anyone. Hey, wait... I think I read that in the book somewhere...
So if they're getting unsportsmanlike, start tossing people. Don't put up with their BS, but don't show them that they're getting a rise out of you. Doing so just eggs them on further. After a few ejections, it will eventually get through their thick skulls to their small brains - play nice, or don't play at all.
I've seen entire leagues ruined by one team coming in and causing problems that were not being addressed by the umpires. The blues weren't checking bats closely (and a number of altered and non-approved bats were never addressed), weren't tossing people when they should, and generally weren't enforcing a good standard of conduct for the players (and, sometimes, themselves). Uphold a higher standard, and encourage your partners to do the same. Otherwise, you're in for a very long year.