Aikido Multiple Attackers and Randori

One feature of aikido is training to defend against multiple attackers, often called taninzudori, or taninzugake. Freestyle (randori, or jiyūwaza) practice with multiple attackers is a key part of most curricula and is required for the higher level ranks. Randori exercises a person's ability to intuitively perform techniques in an unstructured environment. Strategic choice of techniques, based on how they reposition the student relative to other attackers, is important in randori training. For instance, an ura technique might be used to neutralise the current attacker while turning to face attackers approaching from behind.

In Shodokan Aikido, randori differs in that it is not performed with multiple persons with defined roles of defender and attacker, but between two people, where both participants attack, defend, and counter at will. In this respect it resembles judo randori.

Injuries

In applying a technique during training, it is the responsibility of nage to prevent injury to uke by employing a speed and force of application that is commensurate with their partner's proficiency in ukemi. Injuries (especially those to the joints), when they do occur in aikido, are often the result of nage misjudging the ability of uke to receive the throw or pin.

A study of injuries in the martial arts showed that while the type of injuries varied considerably from one art to the other, the differences in overall rates of injury were much less pronounced. Soft tissue injuries are one of the most common types of injuries found within aikido although a few deaths from repetitive "shihōnage" have been reported.

Article source: http://en.wikipedia.org/wiki/Aikido