Career
Born in Essen, Hörster spent his first three seasons as a professional with local Schwarz-Weiß Essen, in the second division. Foreign 1977-1978 he signed with another club in the league, Bayer 04 Leverkusen. After winning promotion to the Bundesliga in 1979, Hörster was an essential defensive unit for Bayer in the following 13 seasons, his lowest input being 24 games in the 1981-1982 campaign.
Hörster retired in June 1991 at the age of 34, with top flight totals of 332 games and 16 goals.
He remained closely associated with Leverkusen in the following years, working as manager (youth teams, reserves, caretaker) and scout. On 16 February 2003, he was appointed main squad manager, leaving his position on 12 May.
All of his three other appearances were also in exhibition games.