A physical education teacher, he never played as a professional, a fact that did not prevent him from earning his 3rd level manager degree – necessary to coach pro teams in France – as valedictorian in 1958.
He led the Strasbourg team to a good run in the Inter-Cities Fairs cup in 1964–1965 ousting AC Milan and FC Barcelona before falling to Manchester United in the quarter-finals.
A year later, he led the Strasbourg side to victory in the Coupe de France, defeating FC Nantes 1–0.
Frantz is also renowned for his talents as a coaching trainer and is considered to be one of the iniators of the "scientific approach" to training in France.
During the 1970s he was responsible of the formation organized for aspiring pro managers by the Fédération Française de Football, where he taught the likes of Aimé Jacquet, Roger Lemerre and Guy Roux.