Fixing Early Extension
The pelvis moves toward the ball. The spine straightens. You block it right or snap hook it.
The Root Cause
Early extension (often called "goat humping") is rarely a flaw in intent; it is usually a subconscious reaction to a clubface that is wide open, or a steep shaft plane. The brain forces you to stand up to shallow the club and give the hands room to flip the face square.
The Balance Board Cure
To rotate the pelvis without early extending, you must push back and up with the lead leg (posting up). If you early extend on the balance board, your center of mass shifts to your toes, the board tips forward aggressively, and you fall off.
Train this movement using the Ground Force Squat drill.