Everyone has different styles. I didn’t hear it that much in youth football, if at all, I don’t even remember it’s all a blur now, but you better believe in high school I heard it plenty.
I just don’t think it’s a big enough deal for some soccer mom to try to humiliate him like that. He’s the coach. If you really have a problem, take it aside privately.
Also the question is, is her problem with the cursing, or that he’s being hard on the kid. I’ll bet it’s 90% that he’s being hard on the kid. And you have to be hard on kids. There’s no two ways about it. Maybe you have a different style, but I know that that’s what I want.