Is a failure to tag on a fly ball a force play
 

And is it treated any differently with different rule sets. I'm specifically wanting clarification on Fed ruleset.

Assuming you are referring to not leaving a base prior to first contact on a caught fly ball, the answer is no in any softball or baseball game.

It is IMPOSSIBLE to have a force out anytime the player who batted the ball is retired prior to the play in question.

If you just read the definition of a force play, you would realize it is impossible. In any rule set.

Aside from case plays that continue to dispel the myth.

Remembering back to when I was first making the transition from "civilian" to umpire, that was one of the first revalations...... That this was NOT a force play.:o

No; it's an appeal play.

People who don't know any better assume it's a force play because it looks similar to one, where a runner is put out by tagging the base he/she is attempting to achieve. But the similarity ends there. As others mention, you can never ever have a force if the batter flies out.

I suspect the question you worded is not the question you meant.

Did you mean - "When a player fails to tag on a fly ball, can the defense get that player out by merely touching the bag while in possession of the ball?"

Or did you mean - "Does retiring a player who failed to tag on a fly ball nullify a run previously scored on the play"

The answers to these two questions are not the same (Yes and No respectively)

This is true for all softball and all baseball codes.