[greymule]

If a runner has legally scored, he can't unscore himself. The standard example is this:

Abel on 3B tags up and scores after Baker hits a long fly ball that is caught. However, Abel thinks he might have left too soon and so returns to 3B as the throw comes in to the infield. Even if Abel stays on 3B with the ball on the mound, the umpire has to direct him off the base. He scored legally and that cannot be undone.

In my original post, I was thinking that maybe the timing would have an effect, but it wouldn't. The runner legally scored on the play and can't unscore.