"Chelsea Dagger" is a song by Scottish rock band The Fratellis. It was released as the second single from their debut studio album, Costello Music (2006), on 28 August 2006. It is named after Jon Fratelli's wife Heather, a burlesque dancer whose stage name – a play on Britney Spears – he borrowed for the song. Fratelli described the tune as "a rock 'n' roll gig in an old speakeasy or something like that."

This song was number 77 on Rolling Stone's list of the 100 Best Songs of 2007. "Chelsea Dagger" has become notable for its usage in sports. It has also been featured in an Amstel Light ad, the movie Run Fatboy Run, an episode of The Inbetweeners and the video game Rock Band 2. The song peaked at number 2 on the Scottish Singles Chart and number 5 on the UK Singles Chart and was certified gold by the British Phonographic Industry in 2016.

"Chelsea Dagger" is used heavily as a sports anthem. The first team to adopt it was Celtic FC, for whom The Fratellis are supporters. It is played at Stamford Bridge after Chelsea wins an important match. Jon Fratelli commented that their use of the song had resulted in the band supporting the club in the Premier League. The Major League Soccer franchise Montreal Impact also play this song after a goal is scored on home field. It is also used by other football teams such as Perth Glory and Juventus when a goal is scored.

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