Question: Situation (in a youth baseball league game): Bases loaded, 1 out.

A ground ball is hit to the shortstop. Runner at 3rd goes home and touches the plate. Runner at 2nd begins to run to 3rd, but seeing the SS with the ball retreats back toward 2nd, but is tagged out. Meanwhile the runner at first had gotten to 2nd base, but seeing the runner ahead of him retreating, began running back to first. He is then tagged out for the 3rd out of the inning. The umpire rules that the run doesn't count, as the runner who had started at first had brought the force play back into effect by retreating.

Was this ruling correct?

Answer: 
As far as I know there are only two cases where there is a force on a runner:

1. The base behind the runner is occupied and a fair ball is hit. This requires every runner to move up a base. The force is removed is the trailing batter/runner is put out.
2. A fly ball is caught all runners are required to tag and the force is removed by tagging. The direction a runner is going has no effect on if there is a force or not.

The last out must be a force out or made before the batter/runner reaches first base for the run not to count. See here for reference:
[Does the run count on a force out if it's the second out of the play AND the first is a non-forced tag out?](https://sports.stackexchange.com/questions/19924/does-the-run-count-on-a-force-out-if-its-the-second-out-of-the-play-and-the-fir)

The question states that the last out was made by "tag" which is not a force play and so I believe the run should count and the ruling is incorrect.
The MLB rulebook isn't that descriptive with the force play:

> 
> A FORCE PLAY is a play in which a runner legally loses his right
>  to occupy a base by reason of the batter becoming a runner.
> 
> 
> 

If we look at the situation and not the history (batter/runner running to or occupying first base, runner #2 between first and second), then we'd certainly agree that the runner #2 has lost the right to first. There is no safety for the runner at first base, so it is reasonable to expect that the force is on at second.

I don't know if there's any information in the umpire guidelines for this situation, but the ruling seems reasonable to me.