dead ball?

Fed Rule: 5-1-1-j - the ball is dead immediately if the fielder intentionally drops a fair fly, line drive or bunt with at least first base occupied.    There is no IF Fly if the batted ball is a line drive or bunt.  Batter out, runners remain on 1st and 2nd.  Runner protected as soon as ump calls dead ball.

There are a few things that can cause play to be killed, this is one of them. The interesting thing is if it had been an IFF then the ball stays live. 

yep, but honestly, it was no where near a fly ball. just hadn't heard of this dead ball, I give that umpire credit, he was right on it and specific. I am glad he was correct too

Gotta admit.  Not sure I ever heard this.  You say the fielder is not allowed to intentionally "drop" a fair fly, line drive or bunt.  Can they just let it fall?  Is it a judgement call by the ump whether he actually dropped it, or just misplayed it?  I am not 100%, but I could have sworn I've seen a bunt pop up intentionally allowed to hit the ground to try to get a DP.

Also, I thought the IFF rule was put in place so that a fielder couldn't intentionally allow a ball to drop and put the runners in a bad position.  If this rule you quote is in place, why would the IFF even be necessary? 

Just wondering.

The fielder can let it fall (in the non-infield fly scenario) and the ball remains live.  If he "gloves" it or guides it to the ground, then the rule applies -- the batter is out and other runners return.

On most or at least a lot of infield flys at the MLB level the defense could still get a DP by letting the ball fall untouched - it would just bounce up to the fielder and hed turn two.  So you need both rules -- but you are right that they are related and there for about the same reasons.

A ball can be allowed to drop with no penalty. Once he gloves it and then allows it to drop, and if it happens you will know, then the ball is dead. The reason it stays live on an IFF is because the BR is automatically out so the runner should know a drop means nothing.