Starting out at non-League club Elmstead,^[1] Foster made his league debut for Leyton Orient in January 1982 whilst still an apprentice. He moved to Nottingham Forest, for a fee of £50,000 in May 1987, making 72 league appearances under manager, Brian Clough.

In September 1989, Foster became manager Lou Macari's second and most expensive signing for West Ham United for £750,000. Never a regular player under Macari, he became so under new manager Billy Bonds in a team which won promotion from the second division in season 1990–91. Foster's time at West Ham is most often associated with scoring a spectacular mid-air volley in an FA Cup Quarter-final versus Everton in March 1991. Everton were in the upper reaches of the First Division (then the top tier) while West Ham were a second-tier side. West Ham won the match 2–1^[2] before being knocked out in the semi-finals by Foster's old club Nottingham Forest. Three seasons broken by regular injury followed and after a projected £400,000 move back to Nottingham Forest fell through, when Foster could not agree terms, he remained at West Ham on a weekly contract. A loan to Notts County followed before he eventually moved, for a fee of £100,000, to Watford in March 1994.^[3]