How late can one swing?

[beerguy55]

I know it may be an impossible scenario - for me it's part curiosity part thought exercise, and I hope some will indulge me.

Two strikes, nobody on base.  Third pitch is a wild curveball, several feet outside...F2 doesn't really try hard to stop it and knowing nobody's on base he either nonchalantly goes to get ball or just puts his hand out for a new ball knowing someone else will collect the other ball.

Seeing this, the batter swings, some point after the ball hits the back fence/wall and starts rolling toward the third base dugout, (and before the umpire gives F2 a new ball), looking for an easy trip to first on a U3K.

At what point is the swing no longer valid for the purposes of having a strike three?

When the ball passes the catcher?  The umpire?

When it hits the wall?

When it stops rolling or is touched by a player?

As some point of judgment where you determine the ball can no longer be legally hit by the batter?

Thanks for humoring me.

[BigBlue4u]

In the judgment of the umpire, was the batter trying to hit the pitch?  I would just add a ball to the count and get on with it.

[The Man in Blue]

Did the batter "strike at the pitch?"

Can't really do that once it has gone by.