I'm a very active guy. I play tennis 4-6 times a week, mainly on clay. I workout almost daily and hit the cardio equipment pretty hard at the gym. This is the second time(different shoes each time) I've formed a blister under a callus. It is on the ball of my right foot. I already wear 2 pairs of socks when I play tennis. Only workout and play tennis in New Balance shoes. Tennis in the New Balance 851 & NB cross trainers for the gym. Anyone know if this is shoe related? Anyone have an suggestions?