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In the Premier League, five yellows mean a 1-game suspension. One red is a 1-game suspension, and two yellows same game = a red.
Their threshold for yellow cards is fairly low - a mild personal foul, arguing with the ref, taunting, stuff like that. Matthews' hit would have equated to a red card. So would Suh's stomp on Rodgers' calf.
If that doesn't slow the player down, he's soon hauled in front of a disciplinary board, to explain why he should stay in the league. If he does a good job arguing, he only misses like 8 games.
Somebody tell me, in 1-syllable words, why the NFL doesn't implement something similar? Would cut into the injuries quite a ways.