First, I want to dispell the myth that Mario wasn't being double teamed. Just because YOU didn't see it, doesn't mean it didn't happen. And in fact, it did.
This happened the entire game. On some plays, they would have the RB stay in for a moment to check if Mario was getting the best of the RT, if not he would flank out for a pass. If so, he would stay in and double him. There's a reason why Charles and McCluster didnt catch my passes like they usually do...
Another method the Chiefs used was to have the TE chip Mario and then have the RT there as backup. Another double team.
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Second, I want to showcase exactly the impact that Mario is making. Just because he is not recording the sack, does not mean that he is not the reason for them. Just like Revis will not get a lot of interceptions.
Take a look at this play. Mario dominates his man so much that he pushes him back into the QB. Cassel feels this, steps up into the pocket where Dareus takes him down. MARIO is the reason for this sack.
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3) Sack
On this next play, Mario's presence leads to Kyle Williams getting to Cassel and causing the in completion. The right guard moves over to help the LT as seen by the arrow. By the time the RG moves back to his spot, Kyle Williams is already past him and on the way to the QB.
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The next play, Mario flat out beats his guy on a beautiful inside move forcing Cassel to release the ball. Incomplete.
This is just a small sampling. But I think you get the point.
Football is a game of inches. Some of the most important players are invisible, but their impact is what wins you the game.