FED Pitcher's Pivot Foot Set Position

[njdevs00cup]

The reason I ask is that I had a right handed pitcher who would constantly change his pivot foot position on the pitching plate based upon whether the batter was right handed or left handed. He would move his pivot foot all the way to the right of the pitching plate when facing a right handed batter and all the way to the left when facing a left handed batter. When facing a right handed batter, only his heel was in contact and when facing a left handed battter, only his toes were in contact.

The base umpire and I were discussing this after the game. I thought I remembered reading in the case book that this was an illegal pitch or a balk with runners on. I may be mistaken and appreciate it if anyone could clear this up. Thank you.