Former NFL Player Keith Browner Sr. Dead at 63

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 stomach problems, was throwing up, felt tired and said he would go to the hospital Tuesday morning.

We're told Keith Sr. was up Tuesday morning getting ready to go to the hospital to get checked out when he curled over the side of a chair and collapsed to the floor next to his girlfriend.

Keith starred on the USC defense in the 1980s and was drafted with the 30th overall pick in the 1984 NFL Draft by the Tampa Bay Buccaneers.

He played linebacker and defensive end in college and the NFL and ended up playing 5 seasons between the Bucs, San Francisco 49ers, Oakland Raiders and San Diego Chargers from 1984 to 1988.

Keith's son played college football at Cal as a defensive end and spent four years in the NFL with the Houston Texans and Chicago Bears.

He is survived by his 5 children ... Keith Jr. and daughters Keicha, Amber, Ashley, and Jordan.

Keith was 63.