Data Dump: Passing First Down Rate and Completion Percentage

by Chase Stuart on October 13, 2018

Doug Williams was a better passer with the Bucs than he gets credit for, particularly in 1979. He easily led the NFL in sack rate, with an absurdly low 1.7%, when the league average was 7.5%. He also averaged 14.7 yards per completion, the 4th-best rate in the league. But Williams completed only 41.8% of his passes, which was bad even for a 2nd-year quarterback in 1979.

The Bucs ranked dead last in completion percentage (42.2%), with the 27th-best team in completion percentage over five percentage points higher at 47.4%. But as I noted last week, passing first down percentage is a more important metric than completion percentage. And because Williams had a remarkable sack rate and was a downfield thrower, the Bucs picked up a first down on 30.7% of all passing plays. In 1979, that ranked a respectable 12th in the 28-team league.

The Bucs were 11.9% below average in completion percentage but 1.2% above average in passing first down percentage. That’s a difference of 13.1%, which is the largest difference between any team’s completion percentage and passing first down rate since 1970. The full results below:

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Rk	Team	Year	Cmp%	Cmp% Rk	Cmp% Ov Avg	1D/PP	1D/PP Rk%	1D Ov Avg%	Pts Rk	PPG vs. Avg	Win%	Grade
1	TAM	1979	42.2%	28	-11.9%	30.7%	12	1.2%	21	-3	0.625	-13.1%
2	ATL	1975	42.5%	26	-9.9%	28.1%	15	-1.1%	19	-3.4	0.286	-8.8%
3	CLE	2014	54.6%	32	-8.1%	33.6%	16	0.6%	27	-3.9	0.438	-8.7%
4	GNB	1972	42.6%	25	-9.1%	28.3%	15	-0.5%	11	1.5	0.714	-8.6%
5	SDG	1974	47.3%	22	-5.2%	31.5%	7	3.2%	20	-3	0.357	-8.3%
6	CAR	2016	54.4%	32	-8.6%	32.4%	20	-0.4%	15	0.3	0.375	-8.2%
7	TAM	2015	58.3%	29	-4.7%	35.8%	3	3.5%	20	-1.4	0.375	-8.2%
8	ARI	2015	62.8%	18	-0.2%	40.2%	1	8%	2	7.8	0.813	-8.1%
9	PIT	1980	51.7%	24	-4.5%	34%	6	3.2%	10	1.5	0.563	-7.8%
10	PIT	1970	39.1%	26	-12.1%	23.5%	24	-4.3%	21	-4.3	0.357	-7.7%

Showing 1 to 10 of 1,414 entries

On the other side of things, we have the 2006 Houston Texans. Credible analysts often cite David Carr’s completion percentage crown that season as a good example of why completion percentage is overrated. The data today backs that up. Yes, Houston ranked 1st in completion percentage in 2006, at 8.6% above average in completion percentage. However, the Texans ranked just 19th in percentage of passing first down rate, 1.3% below average. That 9.9% differential was the second-most extreme since the merger in that direction, ahead of only the ’73 Oilers.

In recent years, the Bucs, Chargers, and Panthers tend to be the teams most underrated by completion percentage. In 2016, those three teams all had a “grade” of negative five percentage points, meaning they were a lot better in passing first down percentage than completion percentage. In 2017, those three were in the top six of teams most underrated by completion percentage.

What stands out to you?

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