Well, Newton's laws say that an object at rest tends to stay at rest unless acted upon by an outside force. In this case, Dawson was the outside force, particularly his foot. When pushing off the ground, the ground pushes back, giving him momentum in the direction of the football. His foot hits the football, which was at rest, sending it in the direction of his momentum. The air resistance and gravity was not enough of a factor to bring the ball down below the cross bar nor enough to reroute it wide. That is how he hit that.
