twelfth man

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
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012