In 1973, as a high school senior, Bannister led his Kennedy High School team to a state championship, pitching 15 wins and 0 losses with a season ERA of 0.00.[2] His performance led to him being selected in the third round (71st overall) of the 1973 Major League Baseball draft by the Oakland Athletics, but he did not sign.[3]
After pitching just seven games in the minors in 1976, Bannister opened the 1977 season with the Astros. He appeared in 24 games (23 starts), going 8–9 with a 4.04 earned run average (ERA).[1] He spent one more season with the Astros before being traded to the Seattle Mariners in exchange for shortstop Craig Reynolds on December 8, 1978.[5] He spent four years in Seattle, with his last year there being perhaps his best. Bannister finished the season 12–13 with a 3.43 ERA in 35 starts, and was selected to the All-Star Game for the first and only time in his career. He also led the American League with 209 strikeouts, a career best.[1] In 1983 and 1985, he led the American League in strikeouts per nine innings with averages of 8.0 and 8.5, respectively.[1]
On December 13, 1982, Bannister signed a five-year contract with the Chicago White Sox as a free agent.[6] During his time in Chicago, he was a solid starting pitcher, averaging 13 wins each year. In his first season with the White Sox, Bannister went 16–10 with a career-low 3.35 ERA in 34 starts, helping the team earn a playoff spot.[1] He also tossed a career-high 11 complete games in 1987, his last season with the White Sox.[1]
On December 10, 1987, Bannister and infielder Dave Cochrane were traded to the Kansas City Royals in exchange for pitchers John Davis, Mélido Pérez, Chuck Mount and Greg Hibbard.[7] Bannister had another solid season in 1988, going 12–13 with a 4.33 ERA in 31 starts.[1] However, in June 1989, he suffered an injury which knocked him out for the rest of the year. Finding no takers on the free agent market, Bannister went to Japan in 1990, playing for the Yakult Swallows. In nine starts for the Swallows, he went 3–2 with a 4.04 ERA.[8]
On December 13, 1990, Bannister signed a minor league contract with the California Angels,[9] where he was converted into a reliever. He recorded a 3.96 ERA in 16 relief appearances with the Angels before being released on August 29.[1] After one last season with the Texas Rangers in 1992, Bannister was released in August, ending his professional career.[1]
Armed with a strong fastball, an excellent slider, and above average curveball, Bannister recorded an average of 6.49 strikeouts per nine innings in his career, but was also shuffled between six different teams in his 15-year career. He gave up more than 30 home runs in four different seasons and was followed by criticism for a reluctance to move hitters off the plate by pitching inside.[citation needed]
In a 15-year major league career, Bannister compiled a 134–143 record, with a 4.06 ERA in 431 games (363 starts). He had 62 complete games in his career, along with 16 shutouts. He amassed 1,723 strikeouts over his career, averaging 147 a year.[1]
