[CelticNHBlue]

Andy makes a good point regarding pre-pitch position and calling position. I will, however, disagree slightly in this situation as to that being the case.

As U3 rotated, your ideal starting position is the calling position on a steal - 3rd base extended, 6'-8' from the bag. The play in the OP is a ground ball to shortstop and a force at 2nd. This calls for U3 to rotate toward center field to get a 90 degree from the throw while backing up a couple steps to your preferred 15'-18' calling depth. (This may require you to move as far as 1st base extended or more if the SS fields the ball in front of the 2nd-3rd baseline.)

I would guess that one reason you lost track of the ball was due to the fact that you were near straight-lined to the throw, another that you were probable a little too close, and finally you rushed the call a little. As mentioned, a lesson learned; one that we have all learned the hard way before.