The phrase "dumb jock" is a stereotype used to describe athletes as being unintelligent or lacking intelligence. It suggests that they prioritize their physical abilities over their mental capabilities. Full definition
It's as if the kids who ran the chess club suddenly had to contend with a bunch of dumb jocks getting a voting membership... and the lunkheads want a kegger. (chazzwrites.com)
He's got the Yorktown dumb jock vote since a majority of the residents don't vote and all they care about is lacrosse. (nystateofpolitics.com)
Hill wrote the stories for the films, so I can assume he played into his persona a bit and made Tatum that good looking but dumb jock frat boy that Hollywood has probably labeled him at some point in his career. (paulstriptothemovies.com)