[10feet]

Very common in Cricket as well: http://en.wikipedia.org/wiki/The_Twelfth_Man

[Someone]

But there, it has a different meaning. The twelfth man can play. http://en.wikipedia.org/wiki/Glossary_of_cricket_terms#T:

Traditionally, the first substitute player who fields when a member of the fielding side is injured. In Test matches, twelve players are named to a team prior to the match, with the final reduction to eleven occurring immediately prior to play commencing on the first day.