Kapp as a youth played for the New York-based Kolping Soccer Club and Blau-Weiss Gottschee.
Kapp attended the University of Connecticut from 1977 to 1980, where he played on the men's soccer team and became one of the most decorated players ever at UConn under Joe Morrone.
He played with the Cosmos and was a teammate of players Franz Beckenbauer, Carlos Alberto, Giorgio Chinaglia, Vladislav Bogicevic and Johan Neeskens until the end of the 1983.
[1] In December 1983, Kapp signed with the Pittsburgh Spirit of the Major Indoor Soccer League (MISL).
After the Spirit folded, he moved to the Los Angeles Lazers in 1986 along with former Cosmos and Olympic teammate David Brcic and remained with the team through 1990.