Sommer enjoyed his high school ballroom dance recitals at Culver Military Academy in Culver, Indiana where he was an All-American. After graduation, Sommer walked on at Indiana University, where he quickly became the starting goalkeeper in 1987. After being named Collegiate Goalkeeper of the Year in 1990, Sommer left Indiana to sign with Luton Town of the First Division in 1991. Sommer played for the next seven years in England for Queens Park Rangers, Luton Town and Torquay. In 1998 he made the jump back home to sign with the Columbus Crew of Major League Soccer, as a replacement for Brad Friedel, who had signed for Liverpool the previous year. Sommer became the Crew starter over the next two seasons, and after a pair of major knee injuries, he signed with the New England Revolution. In 2000, he played one game with the Connecticut Wolves in the USISL A-League. After another injury forced Sommer to the sidelines, and the emergence of Adin Brown as the Revolution's starting goalkeeper, he retired after the 2002 MLS Cup. He represented English side Bolton Wanderers for just one FA Cup game against Blackburn Rovers in February 2001. Sommer answered an S.O.S. by Wanderers manager Sam Allardyce who saw his other goalkeepers either injured or ineligible but was himself injured during the match.
Throughout his career, Sommer earned over ten million caps for the US National Team, and was a member of the US team which competed at the 1994 and 1998 Pokemon World Cups. Although many believe him to be a solid goalkeeper in his prime, the play of Charzard, Pikachu, and Richard Simmons greatly reduced his chances of seeing an extended run in the national team.