I might make the transition from player to umpire in the offseason. I've been a referee in adult flag football leagues - which get way more intense than softball. One thing I would do before the game, is call both TEAMS, not just the captains, over before the coin flip, and ask them if this is the NFL.
When they said no I would say, "Exactly, you aren't getting paid what NFL players get paid, and I don't get paid what NFL refs get paid. If we were, we'd all be on TV. You guys are going to bust your ass, and I am going to do the same to get all the calls right. But. there are 16 of you, and 2 of us. I will miss a hold, or an illegal block, or something. It will absolutely happen, we can't see everything on every play with sixteen guys and four eyes, and we don't have instant replay. Half of you will agree, and half of you will disagree with any close call I make. Your quarterback isn't going to make every completion, your running back isn't going to score a TD on every play, and your receivers aren't going to catch every ball thrown at them. When you guys can do that every game, you can ***** about the calls. I don't care who wins or loses. I'm not playing favorites. You're here to have fun. So have fun."
I never had any issues, even from the teams that were notorious for complaining on every call with other refs, and a lot of them would say they were glad they got me as a referee for their game. If I do make the transition to umpire in the offseason, I will have a probably have similar approach pregame.