Complex sentence: Futen'ō entered professional sumo as a "makushita" (third division) wrestler in January 2003, as he had gained the amateur equivalent of the "yokozuna" title at Nihon University and so was allowed to leapfrog the lower divisions.
Split into simpler sentences: Futen'ō entered professional sumo as a "makushita" (third division) wrestler in January 2003. He had gained the amateur equivalent of the "yokozuna" title at Nihon University, and so was allowed to leapfrog the lower divisions.