Venusian aikido (sometimes called Venusian karate) was an unarmed combat style used frequently by the Third Doctor to defend himself and others.
According to one account, it was created by the Venusians on Venus, which meant it worked best with five arms and five legs. (PROSE: First Frontier) Another account stated that the Doctor himself invented it. (PROSE: Interference - Book One)
It could be used to immobilise an opponent by using pressure points (TV: The Mind of Evil, Inferno) and perform joint locks, throws and kicks. (TV: The Claws of Axos) It tended to use the attacker's own movements against them. (PROSE: Freedom) These were effective against many different humanoid species, but were useless against non-human duplicates and seemed to have no effect on Ogrons or Sontarans. (TV: The Claws of Axos, Day of the Daleks, The Time Warrior)