Minor leagues (1963–66) Duncan was signed as an amateur
free agent by the
Kansas City Athletics in
1963, as a 17-year-old out of
Crawford High School in
San Diego. In his first at-bat as a professional
baseball player, he hit a
home run for the
Daytona Beach Islanders of the
Florida State League. Duncan made his major league debut on May 6,
1964 at the age of 18, becoming the youngest player in the
American League at the time. He was kept in the majors to protect him from being drafted by another team under baseball rules. Duncan returned to the
minor leagues for the next two seasons, first with the
Lewiston Broncs in the Single-A
Northwest League in
Lewiston, Idaho. Midway through the 1965 season,
Rick Monday joined the team. A 19-year-old sophomore center fielder with
Arizona State, Monday had led the Sun Devils to the
1965 College World Series title on June 12 and was the first pick in the
first major league draft four days earlier. After the season, Duncan and Monday entered
boot camp with the
U.S. Marine Corps in
San Diego in September. The following year in 1966, Duncan led the
California League with 46 home runs in 121 games for the
Modesto Reds, the A's affiliate. The second pick in the
1966 MLB draft was another Arizona State center fielder, 20-year-old
Reggie Jackson. He played two weeks in Lewiston then joined Duncan in Modesto in early July, and kept pace with 21 homers in 56 games.
Kansas City/Oakland Athletics (1967–72) Duncan began the
1967 season with the
Birmingham A's but, was brought back up to the major leagues in early June. When his batting average dropped to a .194 in early July, he was returned to Birmingham to work on his hitting. When his hitting showed signs of improvement, Duncan returned to the major leagues in September, along with Jackson and
Joe Rudi. Athletics' team
owner Charlie Finley moved the franchise west to
Oakland for the
1968 season, but Duncan started the season with the
Vancouver Mounties of the
Triple-A Pacific Coast League. Duncan went on to catch the majority of the team's games in 1968. While he possessed good defensive skills, he only managed to
hit for a .191
batting average. Duncan's hitting improved in
1970 to a career-high .259 batting average along with 10 home runs and 29
runs batted in as, he shared catching duties with
Frank Fernández and
Gene Tenace, who was called up to the major leagues late in the season. He also missed time due to his commitment to the military reserves. When Duncan made adverse comments about Finley during the season, the owner fired Athletics manager
John McNamara in October for failing to control his players, despite the team's second-place finish in the
American League Western Division. The
1971 season saw Duncan become the Athletics main catcher, as he guided their
pitching staff to finish second in the league in
earned run average as well as in
strikeouts. Duncan was the catcher for two 20-game winners in 1971, as
Vida Blue won 24 games and
Catfish Hunter won 21 games. Duncan finished the season with a .253 average with 15 home runs, 40 runs batted in while leading American League catchers in
range factor. The Athletics would win the
American League Western Division but, were defeated by the
Baltimore Orioles in the
1971 American League Championship Series.
1972 would be Duncan's best season offensively as he hit 19 home runs with 59 runs batted in, although his batting average slipped to .218. With Duncan
calling the pitches, the Athletics' pitching staff led the league in
winning percentage and in
shutouts and, once again finished second in earned run average as, the team captured their second consecutive Western Division title. Despite Duncan's production, Athletics manager
Dick Williams, a proponent of the platoon system, began using Gene Tenace as the starting catcher during the last month of the season. The Athletics defeated the
Detroit Tigers in the
1972 American League Championship Series and then the
Cincinnati Reds in the
World Series.
Cleveland Indians and Baltimore Orioles (1973–76) Although Duncan joined the Athletics in
spring training, he became embroiled in a contract dispute with Finley. He was traded along with
George Hendrick to the
Cleveland Indians for
Ray Fosse and
Jack Heidemann on March 24, 1973. Duncan became the Indians' starting catcher in
1973 however, he broke his wrist on June 28 and missed two months of the season. He finished the season hitting for a .233 average with 17 home runs and 43 runs batted in while leading American League catchers in range factor. With the Orioles, Duncan shared catching duties with
Elrod Hendricks during the
1975 season before
Rick Dempsey took over as the Orioles starting catcher in
1976. Duncan was dealt from the Orioles to the Chicago White Sox for
Pat Kelly on November 18, 1976. When the White Sox released him in March
1977, he retired as a player at the age of 32. He was respected during his playing career for his defensive skills and for his knowledge of the game of baseball. In spite of his low average he hit 109
home runs, one for every 26.5
at-bats. During his time with the Athletics, he first met future
manager Tony La Russa, then a
utility infielder with the club.
Highlights • Six two-
home run games, his team winning all six. • One five-hit game, including four
singles and a home run against the
Boston Red Sox (July 12, 1972). • A pair of four-hit games, including two
doubles and two singles against the
New York Yankees (May 5, 1970) and a record-tying four consecutive doubles off of
Luis Tiant of the Boston Red Sox (June 30, 1975). In the other 95 games he played in 1975 he hit only three other doubles. • Nineteen three-hit games, with the most impressive being two home runs and a double against the
California Angels (May 25, 1971). • One five-
RBI game, including a three-run home run, a
bases loaded walk, and an RBI single against the
California Angels (September 21, 1969). • Four four-RBI games. • Named to the
American League All-Star team. ==Coaching career ==