I nominate Kasparov and Botvinnik for their plot against Karpov in the first Kasparov-Karpov match. This was reported in the European press at the time and I would be interested to know if anyone is familiar with it.
In a six-win match, Karpov pulled ahead 5-0 with scintillating play.
Kasparov approached Botvinnik for advice and Botvinnik said: "Start drawing games."
Botvinik, as the story goes, knew Karpov took amphetamines before his games.
After 46 or something straight draws, Karpov collapsed into amphetamine psychosis and withdrew from the match due to what was reported as physical and mental exhaustion.