Brosius grew up in Milwaukie, Oregon, where he attended Rex Putnam High School before going to Linfield College. He was drafted by the Oakland Athletics in the 20th round of the 1987 amateur draft and signed on June 9, 1987. He became one of the limited number of players to hit a home run in his first major league game, on August 7, 1991. Brosius was the A's starting third baseman through the mid-1990s, although he played almost 300 games in his Oakland career at other positions, primarily in the outfield. In 1996, he batted .304 with 22 home runs, his best year with Oakland; however, his performace declined in 1997 (his battiong average was only .203), and he was traded to the Yankees after the season for Kenny Rogers, who had struggled mightily in New York. In his first year in the Bronx