the right call?

Question
there was one out and a man on first. I was base umpire and in position just left of pitcher half way between rubber and second.pitcher set turned and threw to first basemen. first basemen jumped up to catch high throw and as he caught ball landed on and blocked the runner who was diving back. he could not reach base and was tagged.I called him safe on obstruction

Answer
That call could actually have gone either way. Obstruction is probably an ok call since the baserunner should have a path to the base. However, you also could have called him out since the first baseman was in the process of fielding the ball (this is the same thing that happens when there's a play at home, and the catcher blocks the plate while fielding the throw, which is perfectly legal).