I do therapy for a living. The fact that he’s throwing a nerf or smaller ball might be planned. The weight of a regulation or bigger ball isn’t that big of a deal, in fact the weight shouldn’t be an issue at all. It’s the gripping he’s working on, so a smaller ball should be harder to grip and hold. So that might be part of his therapy. The fact he’s using a smaller ball shows his gripping is farther along then what it would be with a regulation ball.