Matt Cassel

You gotta fight for your right to party ... and apparently, Rob Gronkowski didn't earn that privilege after getting drafted back in 2010 -- revealing the Patriots were SUPER pissed at him for celebrating on stage during his big night. The future Hall of Famer detailed the hilarious interaction…

Vikings QB Matt Cassel doesn't really view himself as a mentor to newly drafted QB Teddy Bridgewater ... telling TMZ Sports, "I'm just a teammate brotha." Cassel recently signed a new $10 million contract with the Vikings -- which most people took as a sign that he would be starter when the 2014…