September 26 – After Pittsburgh Steelersjourneyman quarterbackTommy Maddox suffered an elbow injury during the 2nd game of the season, rookie quarterback Ben Roethlisberger, the 11th pick in the 2004 NFL draft made his first professional start in a Week 3 game vs the Miami Dolphins, a 13–3 win for the Steelers. Roethlisberger would start the remainder of the season and went 13-0 as a starter, the best start for a rookie quarterback since the 1970 AFL-NFL merger. The Steelers' impressive run would come to an end when they lost to the eventual Super Bowl champion New England Patriots 27–41 in the AFC Championship Game. This season marked the beginning of a new era for the Steelers, as Roethlisberger would lead them to 3 Super Bowl appearances, winning 2 of them. The Steelers also haven't had a losing record since this season as of 2020.
May 15 – Arsenal complete their last game of the Premier League season with a victory, becoming the first team to go unbeaten for a whole season in the top division of English football since Preston North End in 1889.
October 1 – Ichiro Suzuki of the Seattle Mariners gets two base hits to break the 83-year-old record for most hits in a single season. The previous record, held by George Sisler, was 257 hits in a season.
NBA Finals – The Detroit Pistons, in a major upset, defeat the heavily favored Los Angeles Lakers, 4 games to 1. It is the Pistons first NBA title in fourteen years, and the third in franchise history.
The following day, the UConn women follow suit, defeating the Tennessee Lady Volunteers 70–61, making UConn the first school to win both the NCAA Division I men's and women's basketball championships in the same season. UConn's Diana Taurasi is named the Most Outstanding Player of the Final Four.
March 13 – India beat Pakistan in the highest scoring One Day International ever (693 runs), in the opening match of their first Pakistan tour since 1989
April 2 – Zimbabwe Cricket Union announces the retirement of Heath Streak as captain of Zimbabwe. It is later revealed he was sacked, and 15 senior players withdraw from Zimbabwean cricket, citing political interference by Robert Mugabe's government in team selection.
April 12 – West Indies' Brian Lara regains the individual Test innings record from Matthew Hayden with 400 not out in the fourth Test against England in St. John's, Antigua
June 10 – Zimbabwe Cricket Union agrees to abandon any further Test matches in 2004, under pressure from International Cricket Council over substandard teams due to 15 striking players.
February 12 – An independent audit by Arthur Levitt reveals that National Hockey League teams lost a collective US$273 million in 2003, and suggests the league is "on the road to oblivion."
Semifinals and final to Pride GP 2004 heavyweight tournament. The final between, Fedor Emelianenko and Antônio Rodrigo Nogueira ended in a no contest. A rematch for the final was rescheduled for Pride Shockwave 2004.
5 July – the reigning world champions, New Zealand's Silver Ferns, complete 3-0 Test series win over Australia with 53–46 win at Hamilton, New Zealand.
October 16 – in a qualifying match for the UK Championship, Jamie Burnett makes a break of 148 against Leo Fernandez and becomes the first player to achieve a break higher than the nominal maximum of 147 in a professional match.
January 13–14 – World Cup (short course) held at Stockholm
January 18 – Yang Yu sets a world record in the women's 200m butterfly (short course) in Berlin with a time of 2:04.04, exactly four years after the previous record was set.
March 25 – Frédérick Bousquet breaks the world record in the men's 50m freestyle (short course) at New York City, clocking 21.10
