Hitting a ball the has already hit the ground...

[shickenbottom]

Let me see, hmmmmmmmmmmmmmmmmm.

Pitched ball hits the ground, and the batter hits it, defense fields the ball and throws him out at first. Well it's not an illegal pitch (pitcher did nothing wrong prior to delivery), it's not a foul ball (the ball landed in fair territory), it's not an illegally batted ball (batter wasn't out of the box when he hit it), catcher did not interfere with the batter on his swing, rules do not specifically state that a pitched ball that hits the ground is dead or anything. I think you've got a live ball, and an out at 1st, presuming the fielder caught and controlled the ball when he stepped on 1st base.