Sultan:
Update from me, the OP. Kid played a show game this weekend in front of lots of college and pro scouts. Not his best performance, though it wasn't disastrous. But . . .
The Hat Never Came Off!
Miracle! So when he went to get his hat, he asked for a size Small. The smallest they had was a Medium. I think he was a little worried, as I'd told him if it comes off more than twice, he'd be getting a haircut on Monday. Then I changed my mind, as I was afraid he would be more worried about the haircut than the batter, so I told him, don't worry, no matter what happens you're not getting a haircut. Even so, we placed a velcro strip inside the lining, kind of similar to the idea BaseballHS suggested at the beginning. And, not unimportantly, he mashed it down on his head.
I saw it moving a couple times. But the thing never came off. I feel like Sherlock, along with all of you, finally solving the mystery, though the answer lay in plain sight the whole time. Thanks for sharing the Twitter feed, BaseballHS. I had no idea it was such an epidemic.
So if you see it happening on your team, or in your game, just yell: "Mash the freakin' D1 hat down, bruh!!!!" Problem solved. Or if it isn't, get a smaller hat or put something inside the lining, then mash it down. Or if it's your own kid, and you are so inclined, take him to the barber. And still mash it down.