An underhook is a grappling term for a clinch hold that is used to control the opponent. It is performed from any direction by putting an arm under the opponents arm, and holding the opponents midsection or upper body. Having an underhook with one arm is called a single underhook, while having underhooks with both arms is known as double underhooks. The typical response to an underhook is to try to break it, or to establish an overhook.
The double underhooks is considered one of the most dominant positions in the clinch, primarily because they allow for great control of the opponent, and can be used for doing a takedown or throwing the opponent. The double underhooks can be used to advance into a bear hug by locking the hands behind the back, and holding the opponent close to the chest. The opponent typically responds to double underhooks with double overhooks, to prevent the opponent from advancing into the bear hug.