The tactic was named Diablo because it was "devilishly effective" and, some whispered, because it was discovered on a Spanish-language forum under the user "Diablo."
The Diablo tactic is a specific tactical setup for Championship Manager 03/04 built on a that completely breaks the game's match engine.
you are using (e.g., standard 03/04 or a 2021 update)? Which team you are managing?