You have to understand what "Base Line" means. It is the straight line from where a runner is in relationship to the next base he is trying to get to. So, if he rounded hard around third and was 10-12 feet into foul territory (which is typical), the catcher standing on the foul line would not constitute obstruction.
But, I didn't see the play, so the above might be moot.
He wasn't rounding the bag. He was on third and Sappelt hit a grounder to the pitcher.
Wait, then who sent him home? Were the bases loaded? I did not see the play. So can someone fill me in here?