Infield Fly Rule: Runner Advancement & Tagging Up Explained

Question
I know the infield fly rule applies when runners are in forced positions on the bags with less than two outs. The ball is live and the batter is out regardless if the ball is caught or not by the infielder. My question deals with the runners. IFFR says the batter is out and the runners advance at their own peril. On the fly rule do they have to tag up before advancing?

Answer
Michael,

It is easier to get your head around if you look at it this way.  The IFFR only affects the batter.

So, if the ball is caught, yes the runners have to tag.  If it is not caught, they don't have to tag.  The runners treat the situation like any other fly ball that they are not forced to advance on.  

Tom