OBS or Nuthin?
 

Had a play where B/R hits a gapper into left center field. The B/R is of course concentrating on the flight of the ball and takes quite a wide turn around 1st base. The B/R then collides with the 1st baseman who is approx/ 6-8' away from 1st base. This of course causes the B/R to be thrown off stride and stumbles to the ground. I then yell OBS with a delayed dead ball signal and awarded 3rd base w/o being put out.

1st baseman argues that he was quite a sufficient distance away from the base(line) to have made a difference.

My ruling: I told the 1st baseman that there is no official baseline and that it is his responsibility to move out of the B/R's way. He basically just stood there and allowed the B/R to collide with him. I advised him that if he at least made an attempt to move out of the way that there would not have been an OBS.

Opinions on the ruling are welcome.

Thanks.

Your ruling sounds correct, but this part of your explanation is wrong.

The intent of the defender or what the defender was trying to do (other than fielding a batted ball) is irrelevant. If the defender impedes the runner who is legally running the bases, that is obstruction.

This is why the perfect place(s) for F3 on any play in which s/he is not involved is inside the diamond about 5' or more away from the baseline, or about 3' or more in foul territory beyond 1B.

That still puts them in the vicinity of the base for any throwback while staying clear of the areas where the runner may be.

+1