During the Braves' telecast a few days ago, the announcers noted a story from when Harper was 7 years old and playing in a 10U division. Pitcher threw a fastball that he turned on and hit foul well beyond the fence. From that point, all he saw was curves. Harper noted that he needed to listen to what his Dad had been telling him and learn to hit to left field. So, at age 7 he started learning to hit the breaking ball and hit to all fields.
Without even considering how hard he plays, I wonder if his body will hold up from his violent swinging motion.