I have been a professional pitching instructor for 15 years. Youth, HS and College coach. I played AAA with the White Sox. I would say the the toughest fix is when a pitcher over rotates the lead foot. This happens because of “flying open” " rushing" etc. The 3 most important things to work on as a pitcher are direction, staying back, and following through with good arm extension. NOT bending your back… any suggestions, out of the box drills to correct the over rotation. I have a RHP whos tows are at about 11 o’clock striking with his heel. He is very athletic and has no restrictions with hip mobility. Thanks.
How’s his balance and posture coming into front foot strike? is he leaning toward the 1B line?
I’ve had a pitcher or two throw to me while I’m set up on the inside corner for a RHH and have them stride toward me, then after they have dug a landing hole I move back behind the middle of the plate and have them hit the same landing hole. It’s hard to pitch inside if your hips are flying open or you are landing open. Just a thing I try when drawing a stride line doesn’t work.
I have seen over rotation of the hips where the spin momentum carries them open. I would look at how far is his lift leg and hips rotating back before the push off the rubber begins. Also are the shoulders following the hips during this motion, if so then again that rotational momentum is carrying him open. Obviously this is just a guess without video, but is where I would go first based on your symptoms.