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			Two other ways it can happen: 1) substitute comes onto the field, communicates with a teammate (thereby becoming a player) and then leaving the field before the snap.
 
 2) Player goes to the sideline believing that he's been replaced by a substitute.  Then he realizes that he hasn't actually been replaced, and he returns to the field without sitting out a play.
 
 Rules references: 2-27-9, 3-5-2d, and AR 3-5-2-III.
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