Wally,
IMO you could have diffused the situation by simply acknowledging the balk comment the first time they brought it up. These coaches were obviously clueless, so give them a clue. Someting along the lines of, "That's not a balk coach," or "He's fine, look at rule 8," would most likely have ended the comments.
In my games (and I'd like to hear what the rest of you think) as soon as I notice the rule book in hand, they're both gone. You will no doubt be asked, "For what!?!" My reply is simple... "I don't tell you when to hit and run, You're not going to try to give me a rules clinic during the game."
Simply put... I don't show them up, so I expect the same courtesy in return. It doesn't take long for word to get out that you are fair, but will not put up with the shenanigans.
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Now my best ejection occured during a summer wood-bat league game. I was admittedly struggling behind the plate with my strike zone. Both teams were chirping. I had batters looking back at me, pitchers glaring in at me... I was awful!
The pitcher throws a belt high fastball right down the middle... "BALL FOUR," says I. Batter begins to trot to first base, and I notice the pitcher walking toward the catcher. I can tell he's beside himself. F2 meets him half way, F1 sidesteps and is coming in to talk to me. He gets to the cutout and says, "Where's your strikezone tonight?" I reply, "I left it in the parking lot, you can find it while you're out there!" *DONG!* He's gone!
Later that season I had the same team. Manager sends F1 out with the line up. He's laughing on his way to the plate meeting. I look over his shoulder and the whole team is laughing. He hands me the line up and says, "That was the best ejection any of us have ever seen. We voted you the funniest umpire in the league." I was glad to see that this was indeed a new day.