 On October 31, 1921, Mosberg fought a close bout with Gus Franchetti at the Olympia Athletic Club in Philadelphia, that was called a draw by the "Philadelphia Public Ledger".In a rough bout, Mosberg displayed better ringcraft and scored with stronger punches, but Franchetti attacked on his own each time Mosberg built a margin on points, and managed to even the scoring by the close of the bout.On December 26, 1921, Mosberg lost to fellow Jewish boxer Harry "Kid" Brown in a close eight-round newspaper decision of three Philadelphia newspapers before a partisan crowd at the Olympic Athletic Club in Philadelphia.