Entrapment of the boat/paddler on an immoveable object by the force of the water. Bow of the boat held vertically in a steep rapid or waterfall with the nose of the boat trapped.
To be held in place by the current, usually against a rock or other obstruction. It's a dangerous situation for boaters. See Broach and Entrapment.
Held immobile (but not helpless) in a grapple. Opponents other than the character maintaining the pin gain a +4 bonus to attack rolls against a pinned creature.