1980 Seattle Mariners season

The 1980 Seattle Mariners season was their fourth since the franchise creation, and ended the season finishing seventh in the American League West with a record of .360.

Offseason

 * November 1, 1979: Ruppert Jones and Jim Lewis were traded by the Mariners to the New York Yankees for Jim Beattie, Rick Anderson, Juan Beníquez and Jerry Narron.
 * December 6, 1979: Rafael Vásquez, Rob Pietroburgo (minors) and a player to be named later were traded by the Mariners to the Cleveland Indians for Ted Cox. The Mariners completed the deal by sending Larry Anderson to the Indians on March 29, 1980.
 * December 20, 1979: Willie Horton was signed as a free agent by the Mariners.
 * January 11, 1980: 1980 Major League Baseball draft (secondary phase)
 * Bill Mooneyham was drafted by the Mariners in the 1st round (13th pick), but did not sign.
 * Dan Firova was drafted by the Mariners in the 2nd round.

Regular season

 * September 30, 1980: While pitching for the Mariners against the Kansas City Royals, Rick Honeycutt taped a thumbtack to his finger to cut the ball. Royals baserunner Willie Wilson spotted the tack from second base. The umpires investigated and not only found the tack, but also a gash in Honeycutt's forehead. Honeycutt was ejected from the game, suspended for 10 games, and fined.

Notable transactions

 * April 9, 1980: Dave Heaverlo was selected off waivers by the Mariners from the Oakland Athletics.
 * June 14, 1980: Paul Serna was signed by the Mariners as an amateur free agent.
 * June 16, 1980: Casey Parsons was purchased by the Mariners from the San Francisco Giants.

Draft picks

 * June 3, 1980: 1980 Major League Baseball draft
 * Darnell Coles was drafted by the Mariners in the 1st round (6th pick). Player signed June 13, 1980.
 * John Moses was drafted by the Mariners in the 16th round.
 * Ernest Riles was drafted by the Mariners in the 21st round, but did not sign.

Starters by position
''Note: Pos = Position; G = Games played; AB = At bats; H = Hits; Avg. = Batting average; HR = Home runs; RBI = Runs batted in''

Other batters
''Note: G = Games played; AB = At bats; H = Hits; Avg. = Batting average; HR = Home runs; RBI = Runs batted in''

Starting pitchers
Note: G = Games pitched; IP = Innings pitched; W = Wins; L = Losses; ERA = Earned run average; SO = Strikeouts

Other pitchers
Note: G = Games; IP = Innings pitched; W = Wins; L = Losses; ERA = Earned run average; SO = Strikeouts

Relief pitchers
Note: G = Games pitched; W = Wins; L = Losses; SV = Saves; ERA = Earned run average; SO = Strikeouts

Farm system
LEAGUE CO-CHAMPIONS: Bellingham