Forget Mayweather vs. McGregor ... it was YANKEES VS. TIGERS in Detroit -- when Miguel Cabrera got into a fistfight with Yanks catcher, Austin Romine, and the benches cleared!

Here's the backstory .... Tigers pitcher Michael Fulmer had drilled Yankees star, Gary Sanchez, earlier in the game. Yanks reliever Tommy Kahnle retaliated by throwing behind Cabrera. 

Kahnle and Yankees manager, Joe Girardi, were both ejected over the pitch -- but Cabrera was still unhappy and straight socked Romine behind home plate. 

Pandemonium ensued ... the benches cleared -- and the Yanks relievers came SPRINTING from the bullpen to join the melee. 

Cabrera and Romine were both ejected. The game is still underway ...