Mark William Geiger (born August 25, 1974) is an American sports administrator and former soccer referee.

[3] He officiated the Group E game between eventual tournament champions Brazil and Austria at Estadio Metropolitano Roberto Meléndez in Barranquilla.

[20][21] 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 the United States.

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.

[30] Panamanian Football Federation president Pedro Chaluja said the match was "fixed", and he also wanted FIFA and CONCACAF to investigate.

[31] 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.

After studying teaching at Trenton State College, he became a mathematics teacher at Lacey Township High School in Lanoka Harbor, New Jersey, a role that he gave up to become a full-time referee.

While at Lacey Township High School, Geiger was among 103 recipients of the Presidential Award for Excellence in Math and Science Teaching in 2010.