RBBC, Rushing Concentration, and Outliers

by Chase Stuart on June 18, 2017

In 1984, James Wilder had 407 carries for Tampa Bay at a time when the league was only beginning to shift away from running back by committee. In fact, by the end of the ’84 season, three of the highest single-season carry totals in NFL history had taken place that year, with Walter Payton and Eric Dickerson joining Wilder as true workhorses. The ’84 Bucs had the most concentrated rushing attack of any team in an era of increasingly concentrated rushing attacks.

Take a look: in ’84, Wilder had 1,544 rushing yards, which represented 86.94% of all Bucs rushing yards. The square of that is 75.58%; sum the squares of all players who gained rushing yards for Tampa Bay last year, and you get a concentration index of 75.87%.

Player	Rush	Yds	Perc	Sqrd
James Wilder	407	1544	86.94%	75.58%
Steve DeBerg	28	59	3.32%	0.11%
Mel Carver	11	44	2.48%	0.06%
Jack Thompson	5	35	1.97%	0.04%
Adger Armstrong	10	34	1.91%	0.04%
Michael Morton	16	27	1.52%	0.02%
Gerald Carter	1	16	0.9%	0.01%
Scott Dierking	3	14	0.79%	0.01%
George Peoples	1	2	0.11%	0.00%
James Owens	1	1	0.06%	0.00%
Total	483	1776	100%	75.87%

James Wilder was a one man offense

That was a truly remarkable number in the historical context of 1984. It crushed an NFL record set just one year earlier: the ’83 Rams, with a rookie Dickerson, had a rushing concentration index of 65.95%. Only one other team – the ’81 Oilers — had a concentration index of over 60% when the Bucs hit 76% in 1984.

The average team had a rushing concentration index of 35.5%, and the standard deviation among the teams in 1984 was 13.7%. As a result, Tampa Bay’s rushing concentration index was 2.96 standard deviations above average, known as the Z-Score. That was the 2nd most concentrated score from 1946 to 1984, snugly fit in between the 1966 Patriots (2.93) and 1967 Patriots (2.97).

In 1966, the Patriots led the AFL in rushing attempts and featured a two-back offense with Jim Nance (299 carries) and Larry Garron (101 carries). But since Nance averaged 4.9 yards per carry and Garron just 3.2, Nance wound up rushing for about 74% of the Patriots rushing yards that season. In ’67, New England ran less often, but Nance took a larger share of the load. He had 269 carries to Garron’s 46, and had 76% of all Patriots rushing yards in a very RBBC-centric era. From ’66 to ’67, Nance wasn’t just the top RB in the AFL but in all of pro football. Thanks to his heavy workload, he easily outrushed two HOF RBs in the primes of their career during those seasons.

The table below shows each team that had a Z-Score of at least 1.25 in rushing concentration. Here’s how to read it. In 1991, the Cowboys behind Emmitt Smith had 1,726 rushing yards. ^[1]This excludes any player who finished the season with negative rushing yards. The squared result of each player’s percentage — i.e., the concentration index — was 82.3%. The standard deviation among all teams that year was 13.9%, and the league average was just 33.9%, giving the ’91 Cowboys a Z-Score of 3.48. In other words, the ’91 Cowboys’ rushing attack was so concentrated for that season that it was 3.48 standard deviations above average. That’s why it ranks 1st in this metric.

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Rk	Year	Tm	Top RB	Rush Yds	Sqrd	StDev	Lg Avg	Z-Score
1	1991	DAL	Emmitt Smith	1726	82.3%	13.9%	33.9%	3.48
2	1994	DET	Barry Sanders	2080	82.2%	13.3%	40.2%	3.15
3	2007	ARI	Edgerrin James	1441	72.4%	10.3%	40.2%	3.12
4	1999	IND	Edgerrin James	1660	87.7%	15.6%	40.1%	3.06
5	1967	BOS	Jim Nance	1609	58.7%	10%	29.2%	2.97
6	1984	TAM	James Wilder	1776	75.9%	13.7%	35.5%	2.96
7	1966	BOS	Jim Nance	1968	57.8%	9.7%	29.3%	2.93
8	1961	CLE	Jim Brown	2190	48.5%	7.3%	27.4%	2.89
9	2002	BUF	Travis Henry	1615	79.6%	12.5%	44%	2.84
10	1983	RAM	Eric Dickerson	2274	65.9%	11.1%	34.5%	2.84
11	1980	HOU	Earl Campbell	2657	55.8%	9.6%	28.7%	2.83
12	1974	DEN	Otis Armstrong	2165	47.3%	7.3%	26.8%	2.81
13	1960	CLE	Jim Brown	1982	47.5%	7.5%	26.5%	2.81
14	1988	DAL	Herschel Walker	1999	60.1%	10.3%	31.5%	2.78
15	1968	PHI	Tom Woodeshick	1411	48.6%	7.7%	27.4%	2.77
16	2000	IND	Edgerrin James	1861	84.7%	14.9%	44%	2.72
17	2011	JAX	Maurice Jones-Drew	1970	67.3%	11.2%	37%	2.70
18	2014	DAL	DeMarco Murray	2355	63.7%	10.9%	34.9%	2.64
19	1977	CHI	Walter Payton	2811	47.1%	7.5%	27.4%	2.63
20	1981	HOU	Earl Campbell	1737	64%	11.7%	33.5%	2.61

Showing 1 to 20 of 215 entries

It’s impossible to write about rushing concentration and not discuss Edgerrin James. He has six seasons in the top 61, but perhaps more impressively, his teams have 5 of the top 15 most highly concentrated rushing offenses in league history. That’s remarkable. Ditto goes for Jim Brown, whose teams basically finished 1st in 8 of his 9 seasons playing pro football.

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↑1	This excludes any player who finished the season with negative rushing yards.

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