Prof. P.J. O'Sullivan
Brazilian Jiu Jitsu
Upholding the premise that most of the advantage of a larger, stronger opponent comes from superior reach and more powerful strikes, both of which are mitigated when grappling on the ground, Brazilian jiu-jitsu emphasizes getting an opponent to the ground in order to utilize ground fighting techniques and submission holds involving joint-locks and chokeholds.
A more precise way of describing this would be to say that on the ground, physical strength can be offset or enhanced by an experienced grappler who knows how to maximize force using mechanical strength instead of pure physical strength.BJJ permits a wide variety of techniques to take the fight to the ground after taking a grip. While other combat sports, such as Judo and Wrestling almost always uses a takedown to bring an opponent to the ground, in BJJ one option is to "pull guard." This entails obtaining some grip on the opponent and then bringing the fight or match onto the mat by sitting straight down or by jumping and wrapping the legs around the opponent.
Once the opponent is on the ground, a number of maneuvers (and counter-maneuvers) are available to manipulate the opponent into a suitable position for the application of a submission technique. Achieving a dominant position on the ground is one of the hallmarks of the BJJ style, and includes effective use of the guard (a signature position of BJJ) position to defend oneself from bottom (using both submissions and sweeps, with sweeps leading to the possibility of dominant position or an opportunity to pass the guard), and passing the guard to dominate from top position with side control, mount, and back mount positions. This system of maneuvering and manipulation can be likened to a form of kinetic chess when utilized by two experienced practitioners. A submission hold is the equivalent of checkmate in the sport, reflecting a disadvantage which would be extremely difficult to overcome in a fight (such as a dislocated joint or unconsciousness).