So, rather extreme situation to question if the line may not be as black and white as some are contending.
Runner coming into the base train wrecks with a player moving toward her for the tag. The ball drops in between them and both players are knocked back. With complete disregard for each other, the runner dives at the bag and the catcher dives at the ball. Either a) the fielder grasps the ball a split second before the players collide or b) the fielder grasps the ball a split second after they collide.
If this is black and white, in A) I have a second train wreck and the fielder can make the tag. In B) I have obstruction and send the runner back to the previous base. [On the grounds that without the obstruction she is tagged out.] Is that the way you'd like a young ump like myself learn to call this?
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NaughtyKitten