Rule sets / OBR / Not Touching Plate Balk
Not Touching Plate Balk
A pitcher must be in contact with the pitcher's plate when making a pitching motion.
If there is a runner, or runners, it is a balk when the pitcher makes any motion naturally associated with his pitch while he is not touching the pitcher's plate.
If there is a runner, or runners, it is a balk when the pitcher, while touching his plate, makes any motion naturally associated with his pitch and fails to make such delivery.
MLB Umpire Development Manual Authoritative interpretation
The pitcher must be in contact with the pitcher's plate when he makes a pitching motion. If he is not, it is an illegal pitch. If there is a runner, or runners, on base, it is a balk.