[mikesears]

Definition of a substitute
A substitute is a team member who may replace a player or fill a player vacancy. A substitute becomes a player when he enters the field and communicates with a teammate or an official, enters the huddle, is positioned in a formation or participates in the play.

Here's my take. There is no definition for a teammate so I look at a "teammate" as another player who is on the field. I think we can read between the lines when we look at the other defintions.

Definition of a Replace Player
A player becomes a replaced player when he has been notified by a substitute that he is to leave the field. A player is also replaced when the entering substitute becomes a player.

This seems to indicate that the reason a substitute communicates with another teammate is to inform him that he is taking his spot as a player.



There are two requirements for a sub to become a player.

REQUIRED
1) He must enter the field (obviously)

AND TWO (Any or all of these make him a player).

2a) Communicates with a teammate (I interpret this to mean another player) OR
2b) Communicates with an official OR
2c) Enters the huddle OR
2d) Is positioned in a formation OR
2e) Participates in the play OR