Watching runners away from the ball.

[Snorg]

This happened a few years ago. 16-18 yr old regional tournament, OBR, four-man crew (I'm at 2nd). Runner at 1st base off with the pitch, batter grounds to F6. I position myself for a play at 2B. F6 looks at 2B, then thinks better of it and throws to first. I (perhaps because I was used to doing two-man all season) turn to watch the play at 1B. After the play coach calls time, comes to me, and says that his runner was obstructed by F6 after rounding 2B. I admitted to him that I didn't see it. Coach didn't make too a big stink, and that was that......
I know you don't discuss four-man all that often, but what should I have done there? Watch the runner into and around 2B, while I have my back to the ball and a play at first base? When do I turn to find the ball again?

Also, had this been a two-man crew, I have to follow the ball to 1B, so is the PU watching that runner around second?

Just curious, thanks....