I'm sure this is an over simplification, but he needs to look at some video of his swing. A lot of the time, he looks like he's swinging an ax out there, instead of a level on plane swing. It's like he's trying to chop down on the pitch, not square it up. He's never going to win a gold glove at 3rd, but it does kind of look like his arm/shoulder may still be bothering him.