Brock left the CFL after ten seasons and joined the National Football League for the 1985 season. In what would be his only season playing in the NFL, Brock signed with the Los Angeles Rams as a 34-year-old rookie, setting the NFL record for oldest rookie quarterback in history. Despite the team's star running back Eric Dickerson holding out the first two games over a contract dispute, Brock led the team to a 7-0 start, a feat no other quarterback would accomplish in their first season with a team again until Ben Roethlisberger started 13-0 with the Steelers in 2004. Brock led the team to a division title, the #2 seed in the NFC playoffs, and set team rookie records for passing yards (2,658), touchdown passes (16), and passer rating (81.8) (most of his rookie passing records have since been broken). Brock's final game was the 1985 NFC Championship Game against the Chicago Bears, where he only managed 66 yards passing and lost a fumble that Wilber Marshall returned for a touchdown to close out the scoring in a 24-0 game.