Keith Browner Sr. , a standout football player at the University of Southern California who went on to play 5 seasons in the NFL, is dead ... TMZ Sports has learned. Keith died Tuesday morning in San Leandro, CA ... according to his son, Keith Browner Jr . We're told Keith's death was unexpected and sudden ... and the family is shocked. The cause of death is unclear, but we're told it appears he suffered a heart attack. Keith Jr. tells us he talked to his father Monday night and he was having