Dennis Rasmussen was a left-handed pitcher for the San Diego Padres (1983 and 1988–91), New York Yankees (1984–87), Cincinnati Reds (1987–88), Chicago Cubs (1992), and Kansas City Royals (1992–93 and 1995).

Rasmussen was born in Los Angeles and grew up in San Clemente, California. He nearly lost his left foot at the age of 14, when a speeding car knocked him off of his bicycle on Labor Day in 1973, and the fall severed his foot, which was hanging by the Achilles tendon. An emergency room doctor said they would need to amputate, but an orthopedic surgeon was able to save the foot. As a result, he has no cartilage in his left ankle.

Rasmussen attended San Clemente High School. Six months after the injury, he recovered sufficiently to play in the final two games of the season for the junior varsity basketball team. After one year at San Clemente High School, his family moved to Boise, Idaho, and he attended Meridian High School in Meridian, Idaho, for two years. His family moved to Denver, Colorado, and he went to Bear Creek High School in Lakewood, Colorado, for his senior year. He was named All-State in baseball and basketball, and was a member of the doubles team that won the state championship in tennis.

The Pittsburgh Pirates selected Rasmussen in the 18th round of the 1977 Major League Baseball draft, but he did not sign with the Pirates. As he wanted to play college basketball, he enrolled at Creighton University, which offered him a scholarship to play for the Creighton Bluejays men's basketball team. The arrangement with Creighton also allowed him to play college baseball for the Creighton Bluejays baseball team. For the basketball team, he was a forward who played as the sixth man off the bench. For the baseball team, he had a 3–6 win–loss record and a 3.38 earned run average (ERA) with Creighton in his junior year, with 84 strikeouts, a school record, in 61+2⁄3 innings pitched. He was named to the All-Missouri Valley Conference's First Team.