This is a pretty random post.
Over the last six years, teams have rushed 54% of the time on first and ten, and passed 46% of the time, despite the fact that they've gained 7.45 yards per pass attempt and just 4.28 yards per rush attempt. Even if we subtract 45 yards per interception, teams have averaged 5.75 adjusted yards per attempt -- still about a yard and a half better passing than running.
If passing gets better expected results, why do teams run more often than they pass?
There are several answers. The one I'll focus on is variance. Because variance is higher on pass attempts than rush attempts, rushing yards are worth more than passing yards.
Let's use a numerical example to show why.
In this article criticizing the NFL Passer Rating, Allen Barra writes: "Ask yourself this simple question: Would you rather complete two of three passes for nine yards or one of three for 10?"
Barra implies that the answer is obvious. You'd rather have ten yards than nine. And he's right, of course, but only because ten is kind of a magic number in football. Let's change it up slightly and ask if we'd rather have a 1/3 chance on each pass attempt of getting 9 yards, or a 2/3 chance on each pass attempt of getting 4 yards.
I'd take the latter. We have four downs to make ten yards. With a 33.3% completion percentage at 9 yards per completion, we'd have a 40.7% chance of gaining at least ten yards on four attempts. With a 66.7% completion percentage at 4 yards per completion, we'd have a 59.2% chance of gaining at least ten yards on four attempts.
Even though our expected number of yards per play is higher in the first scenario, our expected number of first downs per drive is higher in the second, and that's more important. The reason is the higher variance in the first scenario.
By the same token, an expected 4.28 yards per rush with a lower variance might be worth more than an expected 5.75 adjusted yards per pass with a higher variance.
This is why one oft-repeated criticism of Passer Rating -- that it gives any weight at all to completion percentage -- seems to me off the mark. If two QBs both average 7.0 yards per attempt, the guy with the higher completion percentage will generally be more effective. He'll be more likely to keep the chains moving because he'll produce less variance. (In other words, his passing yards will be more like rushing yards, and will thus be worth more.)
Over the last six years, teams have rushed 54% of the time on first and ten, and passed 46% of the time, despite the fact that they've gained 7.45 yards per pass attempt and just 4.28 yards per rush attempt. Even if we subtract 45 yards per interception, teams have averaged 5.75 adjusted yards per attempt -- still about a yard and a half better passing than running.
If passing gets better expected results, why do teams run more often than they pass?
There are several answers. The one I'll focus on is variance. Because variance is higher on pass attempts than rush attempts, rushing yards are worth more than passing yards.
Let's use a numerical example to show why.
In this article criticizing the NFL Passer Rating, Allen Barra writes: "Ask yourself this simple question: Would you rather complete two of three passes for nine yards or one of three for 10?"
Barra implies that the answer is obvious. You'd rather have ten yards than nine. And he's right, of course, but only because ten is kind of a magic number in football. Let's change it up slightly and ask if we'd rather have a 1/3 chance on each pass attempt of getting 9 yards, or a 2/3 chance on each pass attempt of getting 4 yards.
I'd take the latter. We have four downs to make ten yards. With a 33.3% completion percentage at 9 yards per completion, we'd have a 40.7% chance of gaining at least ten yards on four attempts. With a 66.7% completion percentage at 4 yards per completion, we'd have a 59.2% chance of gaining at least ten yards on four attempts.
Even though our expected number of yards per play is higher in the first scenario, our expected number of first downs per drive is higher in the second, and that's more important. The reason is the higher variance in the first scenario.
By the same token, an expected 4.28 yards per rush with a lower variance might be worth more than an expected 5.75 adjusted yards per pass with a higher variance.
This is why one oft-repeated criticism of Passer Rating -- that it gives any weight at all to completion percentage -- seems to me off the mark. If two QBs both average 7.0 yards per attempt, the guy with the higher completion percentage will generally be more effective. He'll be more likely to keep the chains moving because he'll produce less variance. (In other words, his passing yards will be more like rushing yards, and will thus be worth more.)
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