Pitch hits the ground

Another reason for the rule (from what I've heard) is eliminate those late swings when a person realizes he/she will get a ball because of the pitch not being in the strike zone. I had someone realize the pitch was a bit deep, so he swung, but the ball had already contacted the ground. I called ball, and he said that he swung. Even the catcher started to say it, and I said, it hit the ground before the swing. They looked at me like I was wrong or something. Geesh.