Batter's Box Interference: Understanding the Rules

Question
You are the batter.
As you swing, you hit the catcher's mitt.
The ball is fair.
However, as you swing, you step out of the batter's box.
What's the call?  interference or out and why?
thanks

Answer
Bob,

I am not a rules guy, and I have never had this one come up in a game, so I will refrain from answering with conviction.

My GUESS is interference because the contact with the catchers mitt preceded the ball being hit in the first place.

There are rules experts available--please check with one of them.

Pete