Why is this.....Out / Not Out, in Baseball ?

Basically, if there are two strikes and the batter foul tips one back into the catcher's mitt and the catcher holds on to it..its an out. Obviously a pop up to the catcher is an out. What your talking about..is a foul tip on strike one or two that nicks the bat and the catcher catches it...Its not an out...because that bat does NOT make ENOUGH contact with the ball to be considered a hit. It is just a tip, a nick, etc. Its not contact. That's the rationale for that. Good Question man.