Welcome to the site. A few things...
There are several threads in this forum that you can search using "yips" as your search word. The topic is pretty much covered from A-Z.
What, exactly, are we talking about? Throws only? Staying down on ground balls? Specific situations or positions?
We have a few kids that age in our JV program going thru something similar right now. They are way better players than what their current performance is showing. They are playing tight. I am not saying this applies to your situation but both have dads that are VERY involved and take things very seriously (in a parent capacity, not a coaching capacity). This reflects directly on the player when you watch the them play. They don't look like they are having fun. They are suffering partially from the pressure of this being the time for dads to let go and these dads not being ready to let go. Both of these kids clearly love the game. They have also reached the "transition-to-HS" age where they (and their dads) are hearing additional outside pressures that tell them they have to really push to excel, when, in fact, it is the time when they should be really having fun competing with HS age players, allowing their hard work to shine. Until it is determined that there is a specific problem that may require help of a specialist, make sure you are keeping things fun for him.
