Erratic Shotgun Snaps

What I tell my centers is to lock their wrist, and release the ball when their elbow hits their thigh. If they perform their snap like this, it will be a good snap every time. When they snap their wrist, the ball tends to fly high. They should also focus on taking the ball from the ground to the QB instead of picking it up and going towards their rear end. I hope this makes sense coach, I've taught our entire team how to shotgun snap (all OL need to know how, position players need to for our pat attempts) and this is how it has been done, very successful with it.