Complex sentence: He held the World Bantamweight Championship on May 23,1928, when he defeated Corporal Izzy Schwartz, but unwilling to defend it at the bantamweight limit, he vacated it in January, 1929.
Split into simpler sentences: He held the World Bantamweight Championship on May 23,1928, when he defeated Corporal Izzy Schwartz. Unwilling to defend the title at the bantamweight limit, he vacated it in January, 1929.