Can't seem to find any non-anime video yet, but here is a description:
From Wikipedia, the free encyclopedia
The Dempsey Roll is a boxing technique culled from the aggressive, loping style characteristic to the Heavyweight champion of the 1920s, Jack Dempsey. It is a bobbing, "rolling" move that requires considerable speed and strength of the lower body. The Dempsey Roll begins with a series of dodging and ducking motions, using the abdomen and legs to turn the upper body. During this stage, the head moves in a near figure-eight pattern. As one speeds up, one moves forward a step at a time. Once approaching the opponent, one pushes with the legs and utilizes momentum created by the rolling motion to throw powerful, smooth punches, often hooks, to the body or head—while still moving back and forth in the figure-eight to keep up the momentum and avoid incoming punches. However, the simple and predictable side-to-side movement makes the Dempsey Roll vulnerable to well-aimed counterpunches and head-on shoves.
Long after the end of Dempsey's reign over the boxing world, the Dempsey Roll was used to great effect by boxers with similar builds and styles. Most notable of these was "Iron" Mike Tyson, whose short stature allowed him to duck under opponents' punches using the Roll far more easily than a taller boxer would have been able to, and whose enormous punching power resembled that of Dempsey himself.
Ippo Makunouchi, a fictional character of the anime and manga series Fighting Spirit, uses the Dempsey Roll as his finishing blow. Though highly dramatized in the series, the technique as presented retains its basic principles, strengths and weaknesses.
The boxing character of Street Fighter III, Dudley, has a special move called "Rolling Thunder", which is in fact a speeded up Dempsey Roll.
In addition, Steve Fox (a boxing character in the fighting series Tekken) has a move called the "Cobra Weave" which is also a variation of the Dempsey Roll."
"In case you ever wondered what it's like to be knocked out, it's like waking up from a nightmare only to discover it wasn't a dream." -Forrest Griffin