Moose Haas, born Bryan Edmund Haas on April 22, 1956, in Baltimore, Maryland, embarked on his Major League Baseball career as a right-handed pitcher. He was drafted by the Milwaukee Brewers in the second round of the 1974 MLB Draft. Haas made his debut with the Brewers on September 8, 1976, marking the beginning of his professional journey in the major leagues.

Haas quickly became a reliable presence on the mound for the Brewers. In the late 1970s and early 1980s, he was a consistent starter for the team, known for his control and ability to keep hitters off balance. One of his standout seasons came in 1979 when he posted a 3.27 ERA over 32 games, demonstrating his effectiveness as a pitcher. His performance helped solidify his role in the Brewers' starting rotation.

The 1981 season was particularly memorable for Haas and the Brewers. Despite the season being split due to a players' strike, Haas played a crucial role in helping the Brewers reach the postseason for the first time in franchise history. He pitched effectively in the American League Division Series against the New York Yankees, although the Brewers ultimately fell short.

Haas continued to be a mainstay in the Brewers' rotation throughout the early 1980s. In 1982, he contributed to the Brewers' successful campaign that led them to the World Series. Although the Brewers were defeated by the St. Louis Cardinals in a seven-game series, Haas's efforts throughout the season were instrumental in the team's journey to the championship.

In 1983, Haas achieved a personal milestone by recording a career-high 13 wins. His ability to pitch deep into games and maintain control over his pitches made him a valuable asset to the Brewers. However, as the mid-1980s approached, Haas began to experience some challenges with injuries, which affected his performance and playing time.

In 1986, Haas was traded to the Oakland Athletics, where he continued his career. Although his time with the Athletics was shorter and less impactful than his tenure with the Brewers, he provided veteran leadership and experience to the pitching staff. Haas retired from professional baseball after the 1987 season, concluding a career that spanned over a decade in the major leagues.

Throughout his career, Moose Haas was known for his steady presence on the mound and his ability to adapt to different situations.