Infield Fly Rule and tag-ups

Question
I have a pretty good understanding of the infield fly rule except for this:  do the runners have to tag-up if the infield fly rule is invoked?  For example; say the runners on second and first take their lead-off (prior to the pitch.)  When the fly ball is hit, the runners are still off the bags but staying close because it is a pop fly.  Next, the Ump yells "Infield Fly"- do the runners have to return to the bags before they can advance at their own risk?

Answer
Chris,

The runners do have to return to their bases before they can advance at their own risk if the ball is eventually caught.  They cannot leave their base until the ball is caught (unless they want to be doubled up).

However, if the umpire calls infield fly and the fielder drops the ball, the runners do not have to return.  They can only be doubled off if the ball is caught.

Hope this helps!

Brian