He was a "strong and forceful" player, able to hold the ball up in order to bring other players into the game. Horsfield made his Football League debut with Scarborough as a teenager. Released by the club, he returned to part-time football with Halifax Town, Guiseley and Witton Albion, before a second spell at Halifax saw him help the club regain their Football League status. He moved on to Fulham, with whom he achieved promotion to the First Division, before joining Birmingham City for a club record fee. He played in the final of the 2001 League Cup with Birmingham, and the following season helped them reach the Premier League.