The video link
Baseball Oddities | NYY@TOR: Posada tags Escobar for the out in odd play - Video | MLB.com: Multimedia
It was actually a 4-3 grounder up the middle. Posada never actually got the tag so the out call could have been a baseline or failure to return to first infraction. If the runner had taken off for 2B, Posada might have thrown down to second (since his first appeal of stepping on the bag did not work). A botched rundown might have allowed the runner to get back to first.