I notice in the video that there is a hole in front of the rubber where he plants his pivot foot. Perhaps it’s the hole that his pivot foot is conforming to, and nothing else.
I’ve coached pitchers to do just that - slant the pivot foot slightly towards home plate with the toe. Why? Because this slight adjustment with the pivot foot will accent the body to deliberately change the “bite” on every breaking pitch in a pitcher’s inventory.
If you have a slider and you want it to bite hard - like in a backdoor slider - this is the foot plant that you want to groom. If you have a cutter that you want to bite down hard with - this is the foot plant that you want to groom. Do you want a curve ball that comes in with a late breaking sweep - this is the foot plant that you want to groom.
With fastballs, some pitchers have a greater tendency to go inside with a higher rate of sucess with this kind of pivot foot posture.
How do you know it’s the right thing for you? Take a video camera with you and go through every pitch in your inventory with your standard foot plant. Deliver enough pitches to give you a good sample of what your normal stuff looks like. Then, alter your foot plant and watch the influence on each pitch change - and change it will, big time.
Excellent observation here. Outstanding.