He is predominantly remembered for his first spell with SV Waldhof Mannheim, when he led them to the 2.

Born in Lampertheim, Hesse, Schlappner's early career in football was not particularly eventful.

[1] Schlappner's career as a manager rose to prominence when he was able to lead SV Waldhof Mannheim to win the 2.

During his time with them, he helped establish them within the Bundesliga for the next several seasons and oversaw them through some of their most successful periods in the club's history until he left in 1987.

He moved away from senior management but returned to Asia to help Iran to establish the newly re-branded Iran Pro League during 2000 as well as acting as an adviser for the Mongolian Football Federation in 2006.