There is no clear definition or reference of "three fists and four legs" in the usual context. It may be a martial arts or sports technique, or it may be a specific sports activity or fitness method.

Literally, this phrase may come from some skills in martial arts or sports. Among them, "three fists" may refer to hook, straight fist and swing fist, while "four legs" may refer to hook kick, bounce kick, side kick and leg sweep.

However, this phrase is not a standard or well-known term, and there is no recognized clear definition. In different contexts, there may be different interpretations and meanings. It is suggested to use this term under the guidance of a specific context or specialty to avoid misunderstanding.