'Hard Knocks' Star Riley Bullough: I've Got Country Music Pipes!

He's known as the passionate, expletive-shoutin' fan favorite on HBO's "Hard Knocks" ... but did you know Tampa Bay Bucs player Riley Bullough is an aspiring country music singer?!

You better believe it!!

The ex-Michigan State star joined the guys on the "TMZ Sports" TV show on FS1 to talk about his training camp experiences in front of the camera ... and we asked if there's a secret side to him that wasn't revealed on the show.

That's when Riley spilled the beans about his country music moonlighting ... and we gotta admit, dude sounds legit.