weighted baseballs

I have bought some wieghted baseballs and wondered if they really improve velocity.

Also would it be bad to use them inseason even if you only trained with the lighter ones (underload training)

Weighted balls are a tool like everything else and if you are going to use them in season you have to make sure you integrate it with the rest of your throwing program. As far as using only the underweight balls goes, IMO, underweight balls tend to be more risky than overweight balls so I wouldn’t go with the idea of throwing underweight balls based on the assumption that it will be less risky.