twelfth man

British  

noun

1. a reserve player in a cricket team

2. anything that is regarded as a contributory factor to the success of a football team, esp a large and vocal home support

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Example Sentences

A twelfth man, a former police officer, is accused of offering material support to the group.

From BBC

Seattle's football crowd is knows as "the twelfth man" because they cheer so loud that the visiting team can not talk to each other.

From New York Times

Cricket teams consist of eleven players plus an extra player in the side called the twelfth man, who serves as a substitute in case someone gets injured.

From Time

At the end of Saturday’s opening performance, the curtain calls were greeted with an enthusiastic ovation — but when Speight Jenkins stepped onto the stage, a “Twelfth Man” roar went up that practically lifted the McCaw Hall roof.

From Seattle Times

An ugly conflict was brewing in the early 2000s when Seattle’s loud, zealous fans began to call themselves the team’s “Twelfth Man.”

From Salon