|#4 Ciaran OBrien|
O'Brien played center midfield for four years at Decatur High School in Federal Way, Washington, where he earned NSCAA All-American honors, was a First Team All-South Puget Sound League selection for four straight years, and was selected as the Washington State Gatorade Player of the Year after his senior season.
O'Brien initially played college soccer for the University of San Diego, where he was a NSCAA Freshman All-American and was named to the All-WCC Second Team, before transferring to UC Santa Barbara in his sophomore year. With the UCSB Gauchos, he made the 2007 NCAA Tournament, losing out to national finalists Ohio State. He was named the 2007 Big West Midfielder of the Year with UCSB, as well as the highest scoring player in the Big West. During his college years O'Brien also played for Tacoma Tide of the USL Premier Development League, where his father was head coach.
O'Brien decided to leave UCSB early without graduating, signing a Generation Adidas contract in the process. He was the 5th overall pick in the 2008 MLS SuperDraft, selected by the Colorado Rapids.
O'Brien was sent on loan to USL First Division side, Seattle Sounders, in August 2008 to gain first team experience but was soon recalled and was back with Colorado at the end of August.In June 2009, O'Brien made a season long loan to USL-1 side Austin Aztex. In July 2009, he was signed on a loan from Colorado Rapids by Impact de Montréal until the end if the 2009 USL season.During summer 2010, O'Brien trialed with League of Ireland Premier Division side Sporting Fingal but a loan deal with Colorado could not be agreed.
O'Brien graduated from the MLS Generation Adidas program on November 18, 2010. O'Brien became a MLS free agent when Colorado declined his 2011 contract option and he was not selected in the 2010 MLS Re-Entry Draft.
O'Brien signed with North American Soccer League club Atlanta Silverbacks on March 21, 2011. O'Brien won his first league honors on July 11, 2011, winning the NASL Offensive Player of the Week. Spent time with Carolina RailHawks in 2013.
O'Brien signed with San Antonio Scorpions for the 2013 Fall season.