[Schneed10]

For the uninitiated, here's the very basics on how QBR works.

If you're at your own 20, and it's first and 10, there's a certain expectation for the number of points the average QB can be expected to put up in that situation. Maybe the average QB finishes some drives starting in that position with a FG, maybe finishes some starting there with a TD, maybe some with a punt, and maybe some in a turnover. When you add it all up, maybe the typical QB comes away with 2 points on average in those situations. So we say a 1st and 10 at your 20 is worth 2 expected points on the scoreboard.

Well if you hit a 30 yard pass taking the ball to the 50, and then you have 1st and 10 from there, well you've just improved your odds to score points on this drive significantly. Your chances of at least getting a FG have gone way up, right? And your chances of finishing with a TD have improved, too. So when you look at the average points scored by the average QB on drives starting at 1st and 10 from the 50, the average points scored there might be 3.

So in other words, hitting that 30 yard pass to go from your own 20 to the 50 improved your expected points scored by 1 whole point. You were expected to get 2 points out of the drive when you were at the 20, and you're expected to get 3 out of drive from the 50. The difference is the impact you made on the play.

Now, let's say you're 1st and goal from the 5. The expectation might be you'll get 5 points out of that situation, on average. If you throw a pass and you get the TD, you get credit for scoring 7, so that throw was worth 2 points. Likewise, if you go 3 and out and have to attempt a FG, then your expected points drop from 5 to 3, so you get hit with a -2 expected points for failing to come up with that TD.

So it weights the play you make against the expected outcome given the situation. And then ESPN goes a step further to assign a clutch weighting. If you make a big throw in the 4th quarter when you're down by one score, they weight that much more heavily than if you make a big throw when you're down by 3 TDs in the 4th quarter (garbage time).

Then they take the results and they index them, with 50 being average and 100 being perfect.

So it does a great job of measuring a QB's impact on the likelihood that his team will win the game. Still, there's a factor built in there - if your team protects you well and your receivers get open well, then you're more likely to succeed and end up with a better QBR. So you have to adjust for that.

If you see a QB rated highly in QBR despite a crappy line and mediocre receivers, you should basically consider that QB a god. Andrew Luck jumps out - being 7th in QBR despite that horrendous surrounding cast speaks to just how amazing he is. If he gets a surrounding cast, watch out!

Likewise, Cousins is not the 5th best QB in the league. He has performed that way because our line is boss and our receivers are plentiful. Don't get me wrong, I'd still pay him. But you have to mentally adjust a bit for surrounding cast and circumstances.