Geiger first took up refereeing in 1988. He became a United States Soccer Federation National Referee in 2003 and officiated in Major League Soccer from 2004 to 2018. He has officiated in CONCACAF tournaments since becoming a FIFA referee in 2008, and has officiated Gold Cup and other international tournaments and fixtures. Geiger was selected for the CONCACAF U-20 Championship in 2011, where he refereed the final. Geiger officiated at the 2011 FIFA U-20 World Cup in Colombia. He officiated the Group E game between eventual tournament champions Brazil and Austria at Estadio Metropolitano Roberto Meléndez in Barranquilla. He then took charge of the Group B game between Uruguay and Cameroon at Estadio El Campín in Bogotá. He was appointed to the Round of 16 match between Spain and South Korea at Estadio Palogrande in Manizales. Finally, he refereed the Final with American Assistant Referee Sean Hurd and Canadian Assistant Referee Joe Fletcher, between Brazil and Portugal at Estadio El Campín in Bogotá. This was the first time a referee from the United States has ever officiated a major men's tournament final. Geiger was selected as the Major League Soccer referee of the year for the 2011 season, and then again in 2014. In 2012, Geiger was selected as one of 16 referees to officiate at the 2012 Summer Olympics in London. Geiger took charge of the Group D match between Spain vs. Japan and the quarterfinal between Japan vs. Egypt. In 2013, Geiger was an official at the 2013 CONCACAF Gold Cup. Geiger was selected as CONCACAF's representative referee for the 2013 Club World Cup.
Geiger was one of 25 referees appointed for the 2014 FIFA World Cup in Brazil. Geiger described the assignment to the World Cup as "an immensely proud moment". Geiger officiated the 2014 World Cup Group C match between Colombia and Greece at the Estadio Mineirão in Belo Horizonte; the 2014 World Cup Group B match between Chile and Spain at the Maracanã Stadium in Rio de Janeiro; and the 2014 World Cup Round of 16 match between France and Nigeria at the Estádio Nacional in Brasilia, the first American to referee in the knockout round of a FIFA World Cup.
Geiger was one of 36 referees selected for the 2018 FIFA World Cup, working with a North American crew of Joe Fletcher from Canada and Frank Anderson from USA. Geiger served as referee on three matches at the tournament and was VAR on five matches. Geiger's first assignment was the second group stage match of Group B between Portugal and Morocco. Geiger worked as the VAR In the match between Denmark and Australia. During the match he advised the referee, Antonio Mateu Lahoz, to review a possible handball in the penalty area. After review, Lahoz awarded a penalty kick that allowed the Socceroos to score and secure a 1–1 draw. He subsequently worked as VAR for the Group D match between Argentina and Iceland, the Group G match featuring Belgium and Tunisia and the Round of 16 contest between Uruguay and Portugal before his final assignment in the tournament's Third Place match. Geiger then officiated the Group F third match between South Korea and Germany. South Korea defeated Germany 2–0, but neither team advanced since Sweden defeated Mexico. He then officiated at the Round of 16 game between Colombia and England. England advanced on penalties after a 1–1 draw. Geiger was selected as one of the final 12 referees on the shortlist to officiate the final or third place play-off match, and was ultimately selected to be VAR on the 3rd place match between Belgium and England.
Retirement
On January 9, 2019, Geiger announced that he would retire from refereeing and take up a position within PRO as its director of senior match officials.
