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# The Toolbox: Defensive Success Rates

We continue yesterday's conversation by ... well, picking up a comment I made yesterday in regard to teams whose success rates and leverage rates somehow ended up rather far apart in the rankings despite sort of measuring the same thing:

While success rate and leverage measure basically the same thing, it’s still a bit different.

• Let’s say you gain exactly three yards every play. A gain of three on first-and-10 is not successful, but it results in a “standard down” of 2nd-and-7. Gain three more on 2nd-and-7, and it is not successful, but it results in another “standard down” of 3rd-and-4. Gain three on 3rd-and-4, and it’s not successful but again results in a “standard down” of 4th-and-1. Gain three on fourth-and-1, and it’s a success. That’s a 25% success rate and a 100% leverage rate.
• Let’s say you lose six yards on first down. Unsuccessful, results in a passing down. On 2nd-and-16, you gain 11 yards. Successful, results in a passing down. Gain six yards on third-and-5; success!. That’s a 66.7% success rate, 33.3% leverage rate.

So if a team ranks a lot higher in success rates than leverage (Missouri, Arkansas, Miami), then that perhaps suggests that they were having to recover from occasional first-down issues? Maybe? Just spitballing. If that’s true, then that would suggest that teams with high leverage ranks and lower success rates (Navy, LSU, N.C. State) were able to avoid big losses but had to rely on third down conversions.

I'm going back and forth as to whether that's a valuable way to look at differences in leverage and success rates. I'm open to the idea that this is a purely anecdotal theory, worthless in the overall picture

Anyhoo, just thought I'd put that at the top of the page to continue that line of conversation. Now, to defenses.  Which defenses dominate in the efficiency department, leveraging their opponents into 2nd- and 3rd-and-uncomfortable situations?  Which ones do a little too much bending for a bend-don't-break to work?

We start with the same type of anchor data that we looked at yesterday (only, without the single-game list since ... well, you could just flip "best" with "worst" and see the defensive lists).

Ten Best Single-Season Success Rates
1. TCU (2008): 28.0%
2. Virginia Tech (2006): 28.5%
3. TCU (2009): 28.7%
4. West Virginia (2010): 30.2
5. Alabama (2005): 30.4%
6. Alabama (2009): 30.7%
7. TCU (2006): 31.1%
8. Virginia Tech (2005): 31.3%
9. Oregon State (2007): 31.5%
10. Boise State (2010): 31.7%

TCU, Virginia Tech and Alabama in multiple spots?  Yeah, that sounds about right.  Though Alabama did their biggest damage under two different head coaches, the presence of TCU and Virginia Tech does hint at something I've noticed through quite a few other observations: while offense is cyclical and based on innovation/tinkering and specific sets of talent ... defenses seem to exist at a more consistent level despite turnover on the field.  To drastically over-generalize, talent matters most on offense, coaching matters most on defense.

Ten Worst Single-Season Success Rates
1. UNLV (2010): 57.7%
2. Washington State (2009): 54.9%
3. North Texas (2008): 54.7%
4. Air Force (2006): 53.7%
5. Washington (2008): 52.1%
6. Western Kentucky (2009): 52.0%
7. Texas A&M (2008): 51.7%
8. UTEP (2008): 51.6%
9. UNLV (2009): 51.4%