Plowing over the catcher

[blueump]

Runners coming home from 3rd, in MLB, will freqently try to "run through" the catcher who is standing ready to make a tag. Freqently I see the catcher bracing for the impact by bringing both hands together in front on his body and lowering his own shoulder.

During these high impact collisions, the glove never seems to touch the runner, but the umpire making the call simply waits to determine if the catcher holds onto the ball.

My question is simple (I hope). Does the glove have to tag the runner in this case, or is body contact enough?