Obstruction or not? (A bit long)

Worked a deaf tournament last weekend. Had this unique situation that my partner and I were stumped because we never had it happen before. Here goes:

0 outs, R1 on 1B. B2 hits a very long fly to LCF (if I remember right). R1 can't see the fielder because the 1st baseman is standing right there in the basepath. He positions himself to the point that he is basically in R1's running path. While the ball is on downward flight, R1 gives the 1st baseman a slight push, as if to tell him to move over. 1st baseman moves like a foot over at most, LCF makes the catch. R1 wants to go but the 1st baseman is still in basepath, so R1 doesn't challenge. R1 starts to complain. I called time when the ball came in and talked it over with partner.

Partner said he saw the baseman standing in front, but didn't realize how much in the path he was. We were stumped on how to handle it. I felt that R1 might have had a chance to go to 2nd, but that was hard to measure because the ball was still in flight when all this was happening. What we ended up doing was leaving the runner at 1st (runner and coach very unhappy) and warned the 1st baseman that if he did it again, he would be jacked for USC (1st baseman a little unhappy).

I know this might be a HTBT kind of play, but any input from you folks on the board might help. Thanks.