[greymule]

Also remember that a ball that hits the ground before the catcher secures it is not considered caught. I've seen the catcher and the rest of the defense start off the field after a trapped third strike, while the smart runner makes his way legally to 1B.

And a smart runner will do just as WMB described: hang around the batter's box or, if his dugout is on the 1B side, amble toward the bench and then sprint to 1B at the opportune moment.