Football's Biggest Junk Stat

If you've been in comment threads for any length of time, there's a good chance you've seen me pull my hair out over the use of QB Rating as an evaluation metric. The answer I've probably given you is something along the lines of "QB Rating is football's version of WHIP*. It's a junk stat."

*If you want to see good baseball pitching stats, head to Fangraphs and read up on tRA and FIP.

Let's start off by taking a look at the formula behind one of sports' worst commonly accepted statistics.

 

a = (((Comp/Att) * 100) -30) / 20
b = ((TDs/Att) * 100) / 5
c = (9.5 - ((Int/Att) * 100)) / 4
d = ((Yards/Att) - 3) / 4

a, b, c and d cannot be greater than 2.375 or less than zero.

QB Rating = (a + b + c + d) / .06

 

What we have here is a needlessly convoluted mess that doesn't tell us anything of value. This is a statistic that overvalues completion percentage and doesn't put enough value to actual yardage. Let's do a demonstration.

 

QB #1 goes 35 for 40 and Mark Sanchezes his way to 125 yards, passing for one touchdown and zero interceptions.

QB #2 goes 20 for 40, good for 300 yards. He also had one touchdown and zero interceptions.

Plugging these numbers into PrimeComputing's QB Rating Calculator, we return an 88.02 rating value for QB #1. QB #2, on the other hand, scores a rating of 83.33.

 

Just what has happened here? The first quarterback in this little exercise has been handsomely rewarded for checking down and hitting his outlet receivers. The second quarterback has taken a beating for missing on half of his attempts.

I suspect you're beginning to see the issue now.

QB Rating adores players who put up high completion percentages. The problem with this is that it largely ignores the context of those passes. Why value a quarterback so highly for completing a boatload of passes when that's done next to nothing to move the offense forward? Speaking strictly in terms of moving the ball*, you should want the performance our second hypothetical quarterback put up.  

*And I understand that an argument could be made that a higher completion percentage is valuable because it helps keep the clock running. Overall, I think being able to put up yardage wins out.

This only scratches the surface as to why QB Rating is such a flawed tool. I haven't even discussed that it was designed to correlate to quarterbacks in the 70s or how it ignores the context of the game situation. Is an 80-yard drive and a touchdown pass from Seneca Wallace really all that valuable when you're down by twenty with two minutes left in the game? QB Rating doesn't care.

Edit: Something I left off that Nate Dogg points out, QB Rating gives the quarterback full credit for touchdowns. Is it really fair to do that when someone (say, Justin Forsett) gets the ball in the backfield and jukes the entire defense out of their cleats for 20+ yards on the way to the endzone?

I don't want the takeaway here to be that complex statistics are bad. There are other measures that (while not perfect) do a better job valuing player performance. This stat, on the other hand, is mostly noise. 

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