It could just be a mental thing, especially at that age, young kids take failure a lot harder than teens and grown ups do. He probably just had a few bad games and no he lost all of his confidence. Just let him know that your proud of him as long as he's giving 100 percent. Its just something he has to go through, and he will be a better player because of it. I remember when I was in little league one year out of the blue I struck out almost every single at bat,(going from being the leading hitter on my team the year before). That year was so valuable to me because it gave me thick skin and I learned how to fail. Knowing how to bounce back from failure it the most important part of baseball, because you are going to fail at least 60 percent of the time.