Baseball-Tutorials.com – The one knee pitching drill is similar to the follow through pitching drill because they both start with the pitcher on his knees. The one knee drill begins with only one leg down. The knee he kneels on should be his posting leg, so for right-handed pitchers the right leg and for left-handed pitchers the left leg.
Pitchers go through the whole pitching motion using only their arms. This forces the pitcher to develop proper arm mechanics for the rotation and encourages the pitcher to develop a good follow-through across the body.