IFF Question

[mattmets]

I have a question about the Infield Fly rule....it seems pretty basic but as I got to thinking about it, it became more difficult. I think this is a case where more thinking definitely got less results.

On an IFF, does a runner have to tag up in order to advance?

At first I said "No" because the IFF call removes the force at first, and thus the runners are free to advance as they like. Then I thought about it and the rule says that runners may advance AT THEIR OWN RISK. To me, that means that they must indeed tag up. If the pop-up falls, F4 or F6 (or anyone) could throw to 2B (or any bag) and retire the runner who did not tag because the runner takes the risk of advaning of his own accord. Fortunately I've never had this sitch in a game, but I spent an inning and a half at an MLB game discussing the play with my friend.

Was my gut right and I thought too much, or did I think this one through correctly?