Crosby attended the University of Colorado Boulder, where he played on the Colorado Buffaloes football team from 2003 to 2006. While enrolled at Colorado, he displayed extraordinary leg strength, making a school-record 60-yard field goal against Iowa State in 2004. Crosby's 58-yard field goal against Miami in 2005 was the longest ever kicked in NCAA Division I-A football at sea-level without a tee. In all, Crosby holds 31 school records. Crosby connected on 66 of 88 field goals in total during his college career, and 30 of 34 inside 40 yards.
Crosby also served as the Buffaloes' kickoff specialist, where his knack for forcing touchbacks after touchdowns made him a fan favorite. Overall, 138 of Crosby's 203 career kickoffs were touchbacks, including an 87-yard kickoff touchback from the 20-yard line against Iowa State in 2004. The Sporting News named Crosby to its All-Decade team for the first nine years of the 2000s (decade).
Crosby was a first-team All-Big 12 selection in 2004, 2005, and 2006. Following his junior season in 2005, he was recognized as a unanimous first-team All-American, having received first-team honors from the Associated Press, the Football Writers Association of America, The Sporting News, and Walter Camp Football Foundation. As a senior, he was again selected as a first-team All-American by Pro Football Weekly and the Walter Camp Football Foundation. He was the runner-up for the Lou Groza Award, despite being heavily favored to win. During his senior season, he became the first player in Big 12 Conference history to be named player of the week eight times, and became Colorado's all-time leading scorer, with 308 career points.