Complex sentence: Bowling has a background in amateur boxing with a 9-0 record, in amateur MMA with a 3-1 record and soon began fighting in Toughman-like competitions where he dominated before joining a gym where he was introduced him to mixed martial arts.
Split into simpler sentences: Bowling has a background in amateur boxing with a 9-0 record, having competed and dominated his opponents in Toughman-like competitions. Bowling later joined a gym where he was introduced him to mixed martial arts.