On April 29, 2011, in the first inning against the Toronto Blue Jays, the Yankees right-hander Freddy Garcia threw a low split-finger fastball to Juan Rivera that struck him out swinging.

It was a clear, cool night at Yankee Stadium. The catcher, Russell Martin, was set up on the inside corner of the plate against the right-handed Rivera, anticipating the typical splitter action: a sharp downward break, with perhaps a little tail toward the hitter.

But this pitch, video replays confirm, forced Martin to move his glove about a foot to his right, away from the batter, at the last possible moment.

The game continued without any mention of the pitch. But Mike Fast, then a writer for Baseball Prospectus who happened to be watching on television, noticed the bizarre movement and reached out to a friend, Alan Nathan, a physics professor at the University of Illinois.