Mayfield, a defenseman, was selected by the New York Islanders in the second round (No. 34) of the 2011 NHL Draft. The St. Louis native played two seasons with Youngstown of the United States Hockey League before deciding to follow in his father’s footsteps and attend the University of Denver. After two seasons at Denver, Mayfield made his NHL debut with the Islanders on April 6, 2014. After splitting time between the NHL and AHL for a few seasons, Mayfield’s hard steady physical style solidified his position on the Islanders Blueline leading to him signing a 5 year contract on January 4, 2018.