Bigger, Better, Stronger - Part II

I recently discussed how being a "big" player in the NFL matters, just not in ways that we think. I tested Chip Kelly’s "bigger guys beat up little guys" quip by using BMI to define "bigness" and found two significant, somewhat counter-intuitive results. During the 2013 season, a team increased its chances of winning when 1.) its offense was smaller than the opponent’s defense, and 2.) its linebackers were bigger than the opponent’s tight ends. I received a lot of constructive criticism and feedback about my use of BMI, some of which was warranted, so I took another stab at testing Chip’s "big guy" theory and found more cool results. But first, some quick points about the use of BMI from my previous post.

I chose Body Mass Index as a means to measure "bigness" for a few reasons. First, it combines two readily available measurements for every NFL player: height and weight. There are other metrics we can use to define bigness, like arm length, bone density, and muscle mass, but I couldn’t find anyone who kept those measurements for everyone (at least measurements that included players drafted before 2010). Second, BMI is familiar. Everyone who has taken a health class or been to a doctor’s office has come across it. For this reason, I intentionally avoided any reference to health or obesity because, frankly, there was no need to. The post had nothing to do with either. Third, NFL players are not representative of the general population, so, removed from that context, I ultimately decided that BMI comparisons across like-NFL bodies seemed to make sense.

However, not everyone agreed with me (#Merica). I failed to fully address my reasons for using BMI in favor of another, untested, and unproven metric (which I have used below), and failed to anticipate the resulting connotations. But whatever your feelings on BMI, it’s necessary to reiterate that, when using BMI to define bigness, there are still statistically significant findings. Granted, the findings are not easy to interpret, but that doesn’t change the fact that they exist. The interpretation is half the fun.

Moving on, I’m no stranger to creating my own metrics (see Offensive Efficiency Rate) so I tried with bigness. Rather than use BMI, I used the product of height and weight to define bigness. Here’s the actual formula:

(Player Height x Player Weight) / (Avg NFL Height x Avg NFL Weight) x 10

If you can decipher that, you’ll notice bigness values greater than 10 are above the NFL average and bigness values less than 10 are below the NFL average. More importantly, the bigness values are what you would expect to see. For example, Mychal Kendricks (5’11", 237), who was nearly two BMI units bigger than Connor Barwin (6’3", 253), has a "bigness" value of 9.17 (below the NFL average) and is smaller than Barwin, who has a value of 10.34 (above average). Using this metric, the biggest Eagle is Todd Herremans (6’6", 321) with a bigness score of 13.65, and the smallest is Brandon Boykin (5’9", 183) with a score of 6.88. Team-wise, the three biggest teams in the NFL are Baltimore (10.47), Arizona (10.45) and Tennessee (10.44), and the three smallest teams are Green Bay (9.75), Detroit (9.79), and St. Louis (9.79). The Eagles are the 22^nd biggest team. If you look at this on the surface, it doesn’t seem like bigness values have much to do with team wins. And according to linear regression, indeed they don’t. There is no correlation.

Rank	Team	Bigness	Tight Ends		Linebackers		Secondary		Running Backs		Eagles
1	Baltimore Ravens	10.47	BUF	11.44	NYJ	10.55	NYJ	8.51	TAM	10.98	Todd Herremans	13.65
2	Arizona Cardinals	10.45	NOR	11.20	NWE	10.48	SEA	8.47	NWE	9.75	Jason Peters	13.59
3	Tennessee Titans	10.44	WAS	11.08	KAN	10.41	DAL	8.13	ATL	9.46	Isaac Sopoaga (traded)	12.95
4	Miami Dolphins	10.34	NWE	11.08	BAL	10.37	NOR	8.12	CHI	9.29	Lane Johnson	12.88
5	San Francisco 49ers	10.26	MIN	11.01	HOU	10.19	SFO	8.11	PIT	9.28	Evan Mathis	12.76
6	Kansas City Chiefs	10.24	JAX	10.84	ARI	10.18	TAM	8.09	MIN	9.27	Bennie Logan	12.47
7	Carolina Panthers	10.23	PHI	10.81	CLE	10.12	ATL	8.08	OAK	9.20	Cedric Thornton	12.39
8	New England Patriots	10.19	CAR	10.80	STL	10.09	KAN	8.06	NOR	9.14	Fletcher Cox	12.35
9	New York Jets	10.18	CIN	10.79	PHI	9.98	NYG	8.02	NYG	9.10	Jason Kelce	11.53
10	Cincinnati Bengals	10.16	DET	10.79	WAS	9.95	IND	8.01	SFO	9.10	Trent Cole	11.04
11	Seattle Seahawks	10.16	PIT	10.75	CIN	9.93	MIA	7.97	GNB	8.94	Brent Celek	10.81
12	San Diego Chargers	10.15	SEA	10.75	IND	9.92	ARI	7.95	WAS	8.92	Zach Ertz	10.45
13	New York Giants	10.15	CHI	10.68	SEA	9.89	CIN	7.93	IND	8.86	Connor Barwin	10.34
14	Pittsburgh Steelers	10.13	IND	10.63	PIT	9.89	TEN	7.83	NYJ	8.84	Nick Foles	10.24
15	Chicago Bears	10.13	DAL	10.61	BUF	9.87	PIT	7.82	HOU	8.76	Najee Goode	9.75
16	Oakland Raiders	10.12	DEN	10.54	GNB	9.86	JAX	7.82	SDG	8.76	James Casey	9.61
17	Indianapolis Colts	10.08	ATL	10.54	MIN	9.79	PHI	7.77	CLE	8.76	DeMeco Ryans	9.35
18	Jacksonville Jaguars	10.05	KAN	10.47	SFO	9.78	DET	7.75	JAX	8.70	Mychal Kendricks	9.17
19	Denver Broncos	10.04	SDG	10.43	MIA	9.75	BAL	7.73	KAN	8.64	Bryce Brown	8.87
20	Buffalo Bills	10.03	OAK	10.37	OAK	9.74	CAR	7.72	BAL	8.56	Riley Cooper	8.75
21	Cleveland Browns	9.99	NYG	10.36	TEN	9.74	DEN	7.69	DAL	8.52	Michael Vick	8.56
22	Philadelphia Eagles	9.95	NYJ	10.32	NOR	9.71	OAK	7.67	CAR	8.46	Jason Avant	8.36
23	Atlanta Falcons	9.95	ARI	10.31	SDG	9.65	CHI	7.65	BUF	8.33	LeSean McCoy	8.20
24	Tampa Bay Buccaneers	9.92	GNB	10.28	CAR	9.54	MIN	7.63	SEA	8.32	Nate Allen	8.16
25	Minnesota Vikings	9.92	STL	10.27	NYG	9.52	NWE	7.62	MIA	8.32	Earl Wolff	8.09
26	New Orleans Saints	9.90	SFO	10.22	DAL	9.46	BUF	7.56	CIN	8.32	Patrick Chung	8.01
27	Dallas Cowgirls	9.88	CLE	10.16	TAM	9.43	GNB	7.49	DEN	8.20	Bradley Fletcher	7.80
28	Houston Texans	9.83	BAL	10.11	DEN	9.43	CLE	7.47	PHI	8.20	Cary Williams	7.36
29	Washington Lolskins	9.80	MIA	10.02	JAX	9.29	SDG	7.42	ARI	8.13	DeSean Jackson	7.08
30	St. Louis Rams	9.79	TEN	10.01	ATL	9.26	WAS	7.31	STL	8.13	Roc Carmichael	7.06
31	Detroit Lions	9.79	HOU	9.48	DET	9.09	HOU	7.24	DET	7.96	Brandon Boykin	6.88
32	Green Bay Packers	9.75	TAM	9.12	CHI	9.00	STL	7.19	TEN	7.55
	Average	10.08		10.47		9.88		7.82		8.83		9.95

Next, I used logistic regression to compare individual game outcomes to bigness values (more accurately, bigness margins) across similar, competing position groups: offenses to defenses, offensive lines to defensive lines, wide receivers to cornerbacks, linebackers to tight ends, etc. And there are only two competing position groups that yielded significant results.

Tight End versus Linebacker

This was the most statistically significant finding (p-value less than .01). On average, NFL tight ends (10.47) are larger than linebackers (9.88). Picture Denver’s TE Julius Thomas (6’5", 251 lbs) or Philly’s Zach Ertz (6’5", 249 lbs) versus Carolina’s Luke Kuechly (6’3", 242 lbs). So what kind of advantage do teams with big tight ends have? For every one bigness unit increase in a team’s tight end position group relative to its opponent’s linebacker position group in 2013, a team improved its chances of winning by 51%.

Running Back versus Secondary

I was hesitant to include this because I wasn’t sure if running backs and secondaries were relevant competing position groups. How many times during a game do running backs and corners/safeties actually interact? Not exactly sure (maybe more often than I think?), but the result is still statistically significant (p-value less than .05), so here it is. For every one bigness unit increase in a team’s secondary relative to its opponent’s running backs, that team improved its chances of winning by 30%. On average, NFL secondaries are relatively small (7.82 bigness units) and running backs are slightly larger (8.82 bigness units). Picture Bradley Fletcher (6’1", 196 lbs) and LeSean McCoy (5’10", 215 lbs), both average-sized or below with respect to their position groups. If McCoy breaks free into the secondary, who would you rather have available to stop him, Fletcher or Seattle’s Kam Chancellor(6’3", 232 lbs)? Trick question though… no one can stop Shady!

So what about Brandon Boykin?

That last example leads into a nice point. Obviously, for shits and giggles, I’m taking what Chip Kelly said quite literally. In the NFL, big people don’t always beat up little people. Yes, there do seem to be advantages for bigger tight ends and bigger secondaries, but there is no causation here. Big players may not breed team success any more than team success breeds bigger players. At some point, talent, speed, quickness, intelligence, and technique come into play and limit any advantages afforded by size alone. At some point, David beats Goliath. Which is why, with six interceptions (one returned for a touchdown), two forced fumbles, and of course that game-saving interception against Dallas, Brandon Boykin(g) might be the biggest player on the Eagles roster.

Play big or go home.