Keith Mercer (born 1956) is an English former footballer who played as a striker for Watford, Southend United and Blackpool.
He made his debut at 16 years 125 days old on 15 February 1973 as a substitute against Tranmere Rovers, when he became the youngest ever player to play for the Hornets, a record which still stands.
In the 1977–78 season after he suffered a knee ligament injury in September before a recurrence in December put him out of action for four months.
[3] In 1983 Mercer signed for Blackpool, and was joint top scorer with Paul Stewart in the 1983–84 season as the Seasiders finished sixth in the Fourth Division.
He worked as a taxi-driver in Blackpool and, until returning to Watford, he still attended and supports the Seasiders at Bloomfield Road.