I've read a few of these and there is a distinction that is rarely made, and that is that because a child may only play one sport, that doesn't automatically mean they play it year round.
People should be careful not to conflate "specialization" or one sport players with year-round players. This article does specifically mention year round playing or throwing, so that's not necessarily the case here, but it often is.
I have two boys, 10 and 13(11/14 in March/April), and younger son also plays football. Older son stopped tennis last year, but not really interested in other sports. He's tried basketball, wrestling, but not interested. There is nothing wrong with that, but often get questioned or implied that this is harming him in some manner...it is not, he doesn't play year round.
Anyway, wanted to make that distinction. I also don't really know if the experts know what the best course of action is, other than inaction.