The shovel pin is a quick way to incapacitate someone without breaking them. There are times when injuring your opponent is inappropriate, such as when the attacker is a friend or loved one, who just isn’t thinking clearly due to some unresolved personal issues.
To execute a shovel pin, the opponent must be laying on their side at your feet, facing a away from you, while you have a same-side wrist grab. (While this seems like a contrived situation, this is how most takedowns end.) Opposite-side grab the opponent’s elbow, which should point towards you. (If not, make adjustments as needed.) Then, shift or step-slide forward, as appropriate, to roll the opponent into a prone position, pushing their arm down, into them. The floor prevents the opponent from rolling out in one direction. Their own shoulder joint, which is at the limit of its motion, prevents them from rolling out in the other direction.
It is mathematically possible for an extremely strong opponent to attempt a one-armed pushup, to counteract both gravity and your downward force. In this case, pushing the arm towards the opponent’s other shoulder will stress their shoulder joint to the point of dislocation. (Be advised that causing serious injury to a helpless, incapacitated opponent is illegal, and possibly immoral.)
[Shovel pin, fast and slow from the front and side, and a detail of the grip. ]
When performed correctly, this technique resembles shoveling dirt or snow, thus the name.