Stanfill became the third-youngest player for the Eagles when he made his debut at the Toshiba Super Cup in Tokyo, Japan, against Canada May 25, 2005. He has scored three tries for the Eagles and appeared in both the 2007 and 2011 Rugby World Cups. He captained the Eagles in the 2013 IRB Pacific Nations Cup against Fiji June 19, 2013. Stanfill played at the No. 8 position for Cal during its run as National Champion from 2005-2008, before moving to Australia to play professionally with the Canberra Royals. He then moved to Italy to play for Mogliano in the Super 10. In 2012, Stanfill won the Super League Championship with New York Athletic Club and was named Most Valuable Player in the Final. Stanfill currently plays for Seattle Saracens.