Missing Outside to RHB

My son is 10 and just started pitching in April of this year. He has had a lot of success most of the summer but has struggled in his last few starts. When he misses he almost always misses 6"-8" outside (and sometimes high) to right handed batters. Since his misses are so consistent I believe it’s a mechanical problem. Realizing it’s difficult to say since I don’t have video of him yet, any ideas what he might be doing? I have a hunch he might be opening up early. I think he might be opening up and starting his motion towards the plate before his lead foot plants. Would that cause him to miss outside like he has been doing?

It’s a possibility. Without video it’s really difficult to give advice or suggestions.