Venusian aikido

Venusian aikido (sometimes called Venusian karate) was an unarmed combat style developed on the planet Venus, used frequently by the Doctor to defend himself and others. It was created by the Venusians, which meant it optimally needed 5 arms and 5 legs. (NA: First Frontier)

It could be used to immobilise an opponent by utilising pressure points (DW: The Mind of Evil, Inferno), as well as perform joint locks, throws and kicks. These were effective against many different humanoid species, but seemed useless against non-human duplicates. (DW: The Claws of Axos)

The Third Doctor used it disable Professor Stahlman. He claimed that, if the move was held for a period, it would permanently paralyse the target. (DW: Inferno)

Behind the scenes

 * Barry Letts was opposed to the idea of an aggressive Doctor. Therefore, Terrance Dicks suggested aikido as it has no attacking moves. (DOC: Can You Hear the Earth Scream?)