The 43-year-old football star died last May from a self-inflected gunshot wound to the chest. TMZ reports that his family filed the wrongful death lawsuit today in San Diego, claiming the league willfully hid the truth about the dangers of repetitive blows to the head ... such as those regularly sustained by professional football players.

According to the lawsuit, Seau suffered from chronic traumatic encephalopathy (CTE) from those hits -- a condition that his family claims drove him to suicide.