1990 Seattle Mariners season

The 1990 Seattle Mariners season was the 14th for the Seattle Mariners in Major League Baseball. Under second-year manager Jim Lefebvre, they finished fifth in the American League West at .470. It was the second-best record in the M's history up to that point in time; the win total was one behind the club record set in 1987. The Mariners hit six grand slams, the most in MLB in.

Offseason

 * November 13, 1989: Jeff Schaefer was signed as a free agent by the Mariners.
 * December 7, 1989: Pete O'Brien was signed as free agent by the Mariners.

Regular season

 * June 2: Randy Johnson threw a no-hitter versus the Detroit Tigers, the first for the franchise. He was also the tallest pitcher (6ft 10in) in Major League history to throw a no-hitter. It was the 2101st game in Mariners history, played on a Saturday night in the Kingdome.
 * September 14: Ken Griffey Sr. and Ken Griffey Jr. hit back-to-back home runs in the top of the first inning against the California Angels. Through, it remains the only occurrence of consecutive homers by a father and son in MLB history.

Opening Day starters

 * Scott Bankhead
 * Greg Briley
 * Darnell Coles
 * Alvin Davis
 * Brian Giles
 * Ken Griffey Jr.
 * Jeffrey Leonard
 * Pete O'Brien
 * Harold Reynolds
 * Dave Valle

Notable transactions

 * June 4: 1990 Major League Baseball Draft
 * Marc Newfield was selected by the Mariners in the first round (sixth pick), and he signed on June 10.
 * Bret Boone was selected by the M's in the fifth round, and he signed on June 8.
 * June 18: Darnell Coles was traded by the Mariners to the Detroit Tigers for Tracy Jones.
 * June 19: Mario Díaz was traded by the Seattle Mariners to the New York Mets for Brian Givens.
 * August 29: Ken Griffey, Sr. was signed as a free agent by the Mariners.
 * September 18: Rick Rentería was released by the Mariners.

The Griffeys

 * Ken Griffey, Sr. joined his son (Ken Griffey Jr.) to become the first father and son to play in a game together. The game was played in the Kingdome against the Kansas City Royals on August 31. The Griffeys became the first father-and-son teammates to hit back-to-back home runs on September 14.

Line Score
August 31, Kingdome, Seattle, Washington

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 pitched; 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

 * Source: