Renzo Gracie wrote in his book Mastering Jujitsu: "The classical jujutsu of old Japan appeared to have no common strategy to guide a combatant over the course of a fight. Indeed, this was one of Kano's most fundamental and perceptive criticisms of the classical program." Maeda not only taught the art of judo to Carlos Gracie, but also taught a particular philosophy about the nature of combat developed by Kano, and further refined by Maeda based on his world-wide travels competing against fighters skilled in a wide variety of martial arts.
The book details Maeda's theory as arguing that physical combat could be broken down into distinct phases, such as the striking phase, the grappling phase, the ground phase, etc. Thus, it was a smart fighter's task to keep the fight located in the phase of combat that best suited his own strengths.
Renzo Gracie stated that this was a fundamental influence on the Gracie approach to combat. These strategies were further perfected over time by the Gracies and others, and became prominent in contemporary MMA.
Like judo, BJJ encourages free sparring against a live, resisting opponent. Practitioners therefore have the opportunity to test their skills and develop them under realistic conditions, while minimizing the risk of injury. Also known as "rolling."
Divergence from Kodokan rules
Since judo was introduced to Brazil there have been changes in the rules of sport judo—some to enhance it as a spectator sport, and some for improved safety. Several of these rule changes have greatly de-emphasised the groundwork aspects of judo, and others have reduced the range of joint locks allowed and when they can be applied. Many of the banned techniques are preserved in the judo kata, and are practised to varying extents in different clubs. Brazilian Jiu-Jitsu did not follow many of these changes to judo rules, and this divergence has given it a distinct identity as a martial art, while still being recognizable as a sub-style of judo. Other factors that have contributed towards the stylistic divergence of BJJ from sport judo include the Gracies' desire to create a national martial art, the influence of Brazilian culture, and the Gracies' emphasis on full-contact fighting and self-defense.
BJJ permits all the techniques that judo allows to take the fight to the ground. These include judo's scoring throws as well as judo's non-scoring techniques that it refers to as 'skillful takedowns' (such as the flying armbar.) However, BJJ differs in that it also allows a competitor to drag his opponent to the ground, and also even to drop to the ground himself provided he has first taken a grip. Early Kodokan judo not only allowed all that BJJ now allows, it even allowed a fighter to drop straight to the ground without first taking a grip.
BJJ's different rules set and point scoring mechanisms are designed to give BJJ an arguably more practical emphasis. This is done by rewarding positions of control from which the grappler could strike their opponent (if it weren't for the sport's restrictions against striking.) While judo's greater emphasis on throwing is sometimes criticised as not being as useful in a self-defence situation, the effectiveness of throwing should not be underestimated. This is especially so when performed on a hard surface and with the freedom to throw their opponent in a manner that would cause great injury (being unrestricted in the circumstances by sport judo's requirement to rotate one's opponent onto their back.)