[3] A forward, Sweetzer began his career in the youth system at Queens Park Rangers, before transferring to Fourth Division club Brentford in July 1975.
[3] Aged 18, Sweetzer made his professional debut when he replaced Dave Simmons during the match and scored the first senior goal of his career with a late header in the 2–1 defeat.
[6] Sweetzer began the 1976–77 season with niggling injuries,[3] but after returning to fitness he showed prolific form, scoring 23 goals in 28 appearances to pull the Bees away from what would have been an almost-certain re-election scenario.
[8] During the 1977–78 season, Sweetzer was part of a prolific forward line that also included Steve Phillips and Andrew McCulloch and despite being affected by injuries, he scored 14 goals in 20 appearances.
[6] Sweetzer transferred to high-flying Third Division club Cambridge United for a £30,000 fee in April 1978, a move which reunited him with manager John Docherty, who had signed him at Brentford.