My son is the same age. He went from "most valuable offensive player" on Freshman to the biggest slump he's ever had on the summer team run by JV coaches. Same kids, same opponents he played months earlier. The biggest change we could identify was the coaches attitude. "line drive", "keep the ball out of the air" very little encouragement. Messed with the kid's heads. Yes they have to deal with it but was a bit of a shock. It turned around some when I told him to trust the swing he knows, trust that he knows the game and the situation.