What event held by the Ultimate Fighting Championship was the largest regulated professional MMA event?
Mixed martial arts in Ontario:  This paved the way for the largest regulated professional MMA event, UFC 129, which was held on April 30, 2011 at the Rogers Centre in Toronto. UFC 129: UFC 129: St-Pierre vs. Shields was a mixed martial arts event held by the Ultimate Fighting Championship on Saturday, April 30, 2011 at Rogers Centre in Toronto, Ontario, Canada.
UFC 129