Ex-NFL star Brandon Browner wants his conviction overturned in his attempted murder case -- and he's playing the CTE card at the advice of his new attorney, famed O.J. Simpson prosecutor, Chris Darden.
Remember ... back in December, Browner pled no contest to attempted murder for brutalizing his ex-girlfriend in front of her two children. He was sentenced to 8 years in prison.
Browner has since fired his old lawyer and brought on Darden -- who claims the NFL star got screwed because the old attorney didn't realize Browner wasn't mentally fit to cop a plea.