With a Kettlebell in the rack position take a large step forward. Your goal is to lunge as deep as possible keep your front knee from shooting past your toes while maintaining an upright torso. At the bottom of the lunge press the Kettlebell overhead keep your midline tight and your stance steady. Your arm should be straight, elbow locked out. Lower the bell and stand up by driving your front heel into the ground.
Pushing off of the ball of the foot means you did not step forward far enough. The Kettlebell should be pressed straight up not forward or out to the side.
Be sure that the weight is not changing the movement, if it is the weight is too heavy or you are not ready for a loaded lunge.