Breaking Down the NFL QB Rating
T.O. Whenham of Doc's Sports Predictions
The San Diego game on Sunday was over soon after it started, leaving announcer Phil Simms desperate for something to talk about. That's always dangerous. You can only talk about how good LaDainian Tomlinson is for so long, so Simms had to find something else to drone on about endlessly. He settled on the passer rating. He doesn't like it, as it turns out. I don't like him much, either.
Listening to Simms talk endlessly, I realized that I didn't know everything I could about the passer rating. I know that 158.3 is perfect, anything above 100 is really good, and the 1.3 that Rex Grossman got last week is really bad, but the specifics are a bit sketchy. Or at least they were before I embarked on some research.
The passer rating is the combination of four different categories of statistics - completion percentage, average yards per passing attempt, the ratio of touchdowns per attempt, and interceptions per attempt. In order to weight the four categories equally, each one is calculated differently so that they all have a range between 0 and 2.375. It seems obvious that none of the calculations are going to be straight forward if they are boiled down to such an odd number.
The completion percentage number is determined by dividing the completions by attempts, multiplying the result by 100, subtracting 30, and dividing the whole thing by 20. To be perfect in this category a quarterback would have to complete more than 77.5 percent of his passes.
Average yards per passing attempt is a similarly convoluted equation. You divide total passing yards by attempts, subtract three from the solution, and divide the whole mess by four. A quarterback needs to average more than 12.5 yards per attempt to get a perfect score here.
Touchdowns per attempt is the hardest category to comprehend, but the easiest to calculate. You take the number of touchdowns a quarterback throws, divide it by the number of pass attempts, and multiply the result by 20. You would be perfect if you throw a touchdown slightly more often than once every nine passes. You'd also be a very rich quarterback if you did that consistently.
To determine interceptions per attempt you start at 2.375 and work backwards. You divide interceptions by attempts, multiply it by 25 and subtract all that from 2.375. Since you'd have to go a whole season without throwing an interception to be perfect here, it's no wonder that a 158.3 is practically impossible.
Once you have these four numbers you have to combine them into something that makes sense, or at least something that makes a bit more sense than four decimals does. To get the passer rating you add together the four numbers, divide the result by six, and multiply it by 100. Does your head hurt yet?
Simms' biggest complaint was that the rating doesn't give a complete picture of how a quarterback plays. Like most things Simms says, that's a pretty ridiculous comment. He's right, but it isn't meant to give a complete picture. It's a passer rating, so it is only an indicator of how well a quarterback has been passing. Where we get into trouble is when we call the passer rating a quarterback rating and assume it means more than it actually does. It would be like complaining that a defensive player's sack total doesn't accurately tell us how good he is at covering receivers. It doesn't, but that's not what it is designed for.
Because of that limitation of the passer rating, it obviously means that it is more important that a pure pocket passer, like Dan Marino, has a higher rating to be as effective as a scrambling quarterback, like Michael Vick. Because of that, comparing two quarterback's passer ratings in isolation does nothing to tell us which one is the better player. Just the better passer. The added value of a quarterback's rushing yards isn't considered.
If last weekend was in any way a typical game, the passer rating isn't much of a predictor of the outcome of games, either. There were nine games played with two established quarterbacks that have played a significant portion of the season for their teams. The higher rated passer only covered in four of the nine.
Despite that, it only makes sense that the passer rating can be a valuable tool in your handicapping, and there's one stat that gives us the clue to how to do that. Three of the top four rated active passers covered in their games this weekend, and the fourth, Tony Romo, lost to a higher-rated QB. They didn't cover because of their higher rating, but their higher rating is one reason why their teams were successful. Or, more directly, it's one indicator that they play for good teams, or teams with good offenses, at least. Beyond the effectiveness of the quarterback, the passer rating is a good quick indicator of the effectiveness of a team's passing game. It measures yards, touchdowns, interceptions and accuracy. Using the rating, combined with a small handful of other stats like yards per rush, defensive yards allowed, touchdowns and average margin of victory, can very quickly help you isolate the games that are potentially mismatches, especially if they are teams you aren't as familiar with. None of those stats, when used alone, tells the whole story, but the passer rating effectively combines a whole bunch of data into one easy to digest, and easy to compare, figure. Surely you can see the value in that.
So, there you have it. The passer rating is a bit confusing, and calculating it by hand would be incredibly painful, but it can be another useful tool for you to use in your handicapping. And it's not nearly as defective as Phil Simms says it is. He just doesn't bother to understand it.