Plummer was signed by the San Diego Chargers as a free agent in 1986 after playing three years in the USFL.

After going undrafted in the 1983 NFL draft, Plummer joined the Oakland Invaders of the USFL.

After the USFL folded in 1985, Plummer was signed by the San Diego Chargers.

He played his final four seasons of his career with the 49ers and was a member of the 49ers Super Bowl XXIX victory over the Chargers.

From 1998 until April 2011, Plummer was a color analyst for KNBR 49ers game broadcasts.