Baritsu

Baritsu was a Japanese martial arts technique emphasising the use of hands. One account described it as "chiefly notable as having been practiced by the fictional Sherlock Holmes"; (GAME: ) many accounts showed that Holmes was not fictional, but a real person within the Doctor's universe (PROSE:, etc.) until he was fictionalised by contact with The Book of the Enemy during the War in Heaven. (PROSE: ) By 1885, Thomas Carruthers, Sir Reginald Carruthers's son, had some skill at baritsu. (GAME: )

Behind the scenes
The Iytean Menace treats Sherlock Holmes as being fictional in the Doctor's universe, but suggests that baritsu was nevertheless a real, if obscure, martial arts technique incorporated into the books. In contrast, in the real world, baritsua was a fictional creation of Arthur Conan Doyle's, most likely inspired by the similarly-named, which actually existed (though it was only invented in 1899, rendering its presence impossible in 1885, the year most of the events of The Iytean Menace take place).