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Doubling up is the act of throwing two successive blows with the same hand, and can be extended into tripling up, quadrupling up or to any number imaginable - limited only by speed, ambition and arm cramp. The term Lever Punch or Crowbar punch was coined by Soviet Boxing Team Head Coach K. V. Gradapolov in his "Tactics of the Foreign Masters" to describe the legendary black pugilist Peter Jackson's seemingly unique tactic of throwing a hard left hook and without drawing his shoulders back completely throwing another one immediately afterward. This action served to break the opponents guard and concentration as after a hard left hook a hard right punch is almost always expected. The second punch did not matter much to Jackson who simply used it to "lever" open some space in which to fire his powerful right hand, but in recent years it has been possible for the second or third successive punch off of one hand to be used as a damaging blow. A brilliant example of "doubling up" or "lever punches" is Manny Pacquiao's fight with David Diaz:
Manny Pacquiao vs. David Diaz (Highlights) (via ErraticBoxing)
Manny Pacquiao throughout his career had experienced the advantage of being a southpaw - awkward and unseen by most fighters with savvy managers. Against Diaz he fought another southpaw - effectively neutralizing Pacquiao's ability to lead with his left hand. As a southpaw against an orthodox fighter it becomes a contest of power punches seemingly as both sides find it much easier to land a straight with their rear hand (usually their power hand) than with their jab. Jabbing in a contest involving a southpaw and an orthodox fighter is usually largely ineffective unless one participant fights with their lead hand and shoulder down as Diego Sanchez made the mistake of doing against Martin Kampmann a few months back. In this fight Manny had to prove he could fight with his lead hand, and he did it VERY convincingly. At 0:25 Pacquiao uses a slapping lead hook to jump to the side of Diaz, following it with a short uppercut off of the same hand, bringing Diaz's head up for a hook off of his rear, left hand. Manny lands a lead uppercut to the body followed immediately by a lead uppercut to the head at 0:38. By not bringing his hand back to his guard in between Manny is able to bring the punch through Diaz's blind angle, the point down by his feet that he cannot see through his peripheral vision, and so the punch lands with surprise and good effect. Emmanuel Steward - a far wiser man than most in combat sports - breaks down the combination in slow motion at 1:00 noting it's rarity even in modern boxing. Pacquiao again doubles up later in the fight, this time using a jab to lead uppercut combination that lands flush at 1:43 of the video.
Classic Tyson.Bruno vs Tyson part 2 of 2 (via DundeeArabBastard)
Another beautiful example of doubling up from the boxing world is Mike Tyson's famous combination of the jab, rear hook to the body and rear uppercut. He used this to effectively finish tough British heavyweight and all around nice guy, Frank Bruno. At 9:37 Mike has had Bruno reeling but has failed to finish by swarming on him, so he takes a step back and reconsiders his strategy. Pushing Bruno against the ropes he sinks the right hook to the body and immediately follows up with the right uppercut. Again as the punch had started down by Bruno's trunks, Tyson's uppercut was not telegraphed in the usual way by his glove leaving his own chin and dropping below his shoulders.