The principle a 'concussion sub' would reflect is that a team which has lost a player for an entire game as a result of severe foul play should not be worse off than the offending player's team. I like the original suggestion on here that it would be available for a reportable offence. That is an offence the umpire deems serious enough to warrant review, without condemning the player. It works most logically for concussion above other injuries because there is an accepted protocol for assessing concussion and a diagnosis mandates a player missing the rest of the game. Similar decisions about non-concussion injuries would be more subjective and liable to be abused.
The 'red card' reflects the same principle, but is problematic because there is a question as to where to draw the line of severity and applying it consistently.
The 'red card' reflects the same principle, but is problematic because there is a question as to where to draw the line of severity and applying it consistently.

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