Long Tunnel Tee

The best way to tell if a player is staying "through" the ball is to watch the rotation of the ball as it comes off the bat. The ball's rotation will tell us everything we need to know about the swing. Ideally, the ball will come off the bat with backspin; meaning, the player stayed through the point of contact, behind the ball. A ball with hook spin is a ball the player "got around." A ball with flair spin is a ball that the player was inside but "cut off his swing" before extension. Long Tunnell tee is the best way to gauge this. Check the video.