When is a swing no longer a strike?

[DaveASA/FED]

Ok pitch is low and away, got a slapper she tucks the bat and runs up in box, R1 stealing 2nd I am BU, I watch as I am running to 2nd and girl still has bat tucked as F2 is reaching into glove to get ball for throw, so I take attention to upcoming play at 2nd.

Now after play at 2nd (safe) the defense is wanting to check a swing, I say "no" and give a safe signal. Defense is upset but we go on, inbetween innings PU is taking a sub from offense and asks coach "did your slapper swing" he says well it was more like a practice swing after the pitch.

Like I said as I am running to cover the steal at 2nd I am watching the action at plate to be able to answer for a checked swing....and she did not move the bat at least till after the catcher had the ball in glove and was starting to pull it out for a throw.

So the question is....when is a swing no longer a strike? FYI there was no intent to interfere with the play on the runner, I know that is a possibility if done "right" but it was so far outside and in the dirt that PU was tracking the ball and the F2 had a clear area to throw the ball.