Points scored for an O and points allowed for a D are always going to be the gold standard for the measure of a unit, but after points what else do you look at? 3rd downs tend to be a good secondary measure for the performance of a D (stopping them) and an O (converting them).
Good defenses force a lot of 3rd downs. Great defenses force a lot of "3rd and long"s. All-time level defenses force punts on 75% of 3rd downs. The longer the distance, the easier it is to stop 3rd down conversions. Right now the Chiefs are only allowed 25.8% conversion on 3rd downs. One huge factor in this is that so far this year 64% of the 3rd downs that the Chiefs have forced have been 7 or more yards needed to gain ("and long"s). On these "and long" situations that Chiefs have only allowed 19.5% conversion. This is similar to last year's Broncos during the 11 game winning streak, who only allowed 13.6% conversion on 3rd and long. The NFL.com stat database goes back only to 1990 for defensive 3rd down conversion but here are the top single season defensive performances in this stat (I would have loved to see how the 85 Bears or the Orange Crush did):
- 2013 Chiefs (through 9 games) - 25.8%
- 1991 Saints - 26.0%
- 1998 Faiders - 26.3%
- 1992 Cowboys - 27.2%
- 2003 Titans - 27.7%
- 1994 Cardinals - 27.8%
- 1998 Dolphins - 28.8%
- 2006 Ravens - 28.8%
- 2003 Ravens - 29.3%
- 1991 Eagles - 29.8%
That's every team since 1990 to finish the season allowing less than 30% conversion on 3rd down. There are two key points: Most of these teams did this under the old rules for defensive backs/pass interference (these rules changed in 2004). Secondly, even prior to 2004, it didn't happen very often. 24 seasons x 32 teams (can't remember when we added the expansion teams) = 768 chances. 9 instances in 768 chances is 1.2% and it has only occurred thrice (for a full season) this century. So what the Chiefs have done this season defensively on 3rd down has been remarkable - there is no denying that - but there is still the question of whether it is sustainable.
Since numbers don't occur in a vacuum we need to look at what the 9 offenses that the Chiefs have faced have been able to do on 3rd down so far this season
|Team||3rd down %||NFL Rank|
Note that the four remaining opponents are shown at the bottom in bold. Of their first 9 opponents only two are currently in the top half of the league in converting on 3rd down. Their D has feasted on the weakest 3rd down converting offenses in the league missing only the Rams (27th) and the Cards (31st) for a complete set of the "bottom 7". Playing 5 of their last 7 games against teams that have so far this season been in the top 4 in the league in 3rd down conversion %, SHOULD cause the KC 3rd down stop number to increase. Historically speaking the team that leads the league in 3rd down conversion % this century has been at roughly 31% with 03 and 06 being the exceptions. If I had to wager, I'd guess that they will still lead the league in this stat by the end of the season, but their number will go up to roughly 30%.
Ok, so 3rd down conversion % allowed is interesting and all, but does it have any correlation to points allowed? Well, yes, a decent correlation. This century the total correlation between 3rd down % allowed and points allowed is 0.466. Here are the correlation values going back to the turn of the century. As always, correlation is not causation
Most years there is a fairly strong correlation - 05 and 10 being the two exceptions. So teams that stop their opponents on 3rd down are better at stopping their opponents from scoring. Well, duh! Digging more deeply into this - Where have the top scoring Ds ranked in terms of 3rd down conversion allowed so far this century?
Year - top scoring D - ranking in 3rd down conversion - actual 3rd down conversion % allowed
- 2000 Ravens - 5th (34%)
- 2001 Bears - 11th (36%)
- 2002 Bucs - 3rd (34%)
- 2003 Pats - 7th (34%)
- 2004 Steelers - 6th (33%)
- 2005 Bears - 2nd (32%)
- 2006 Ravens - 1st (29%)
- 2007 Colts - 30th (45%)
- 2008 Steelers - 1st (31%)
- 2009 Jets - 1st (32%)
- 2010 Steelers - 3rd (34%)
- 2011 49ers - 11th (35%)
- 2012 Seahawks - 17th (38%)
- 2013 (so far) KC - 1st (26%)
So where does KC finish the season in this stat? They have a substantial lead over the 2nd best team in terms of 3rd down conversion % allowed (Lions are at 31.4%), so their % could take a fairly big hit in one or two games and they could still end up leading the league in this category. For example if the Broncos convert 8 of 15 3rd downs on Sunday night (slightly above season average for the Broncos), KC's % would go up to 28.9% allowed. This would most likely still leave them in the lead in this stat, but their lead would have shrunk dramatically.
On the offensive side of the ball, teams can score well without being great on 3rd down (chunk offenses), but again their is a pretty good correlation. 3rd down % correlation to points scored
The average for this century is 0.68. So offensively there is a stronger correlation to scoring with 3rd down conversions than there is defensively. The other thing to notice, relative to the defensive correlation, is that there are no outlier years here. This correlation looks to be much more stable than the corresponding defensive one.
If you look at some other team offensive stats, yards per play actually has an ever stronger correlation to scoring - 0.81 average for this century. So far this season the Broncos lead the league in scoring, 3rd down conversion and yards per play. If you dig deeper, you find that there are even more stats that have a stronger correlation to scoring than 3rd down conversion. First downs per game and QB rating also have a stronger correlation to scoring than 3rd down conversion %. Currently the Broncos also lead the league in those two stats as well.
I did not do any deeper digging defensively to see if there is a greater correlation with any other stat to points allowed. Someone else can jump on that if they want to.