Premise: Love in the Ring (German:Liebe im Ring) is a 1930 German sports film directed by Reinhold Schünzel and starring Max Schmeling, Renate Müller and Olga Tschechowa. Schmeling was a leading German boxer of the 1930s, and the film attempted to capitalise on this. Schmeling later appeared in another boxing-themed film in "Knockout" (1935).
Hypothesis: Max Schmeling only starred in these two movies in his entire career