CARRIE UNDERWOOD'S husband MIKE FISHER is a total bad boy.  And I mean that in a good way.  Mike dropped the gloves and went toe-to-toe with an opponent who made a cheap shot hit on his fellow Nashville Predators teammate.

It happened Sunday during the playoff game against the Anaheim Ducks . . . and Carrie was in the skybox watching.  I have no idea if she's seen Mike mix it up like that before . . . but she DID look a bit nervous.