Sunday, July 10, 2016

Defensive Net Points Allowed 2015

By John Turney
Almost all, if not all, football stats are skewed in some way, there are so many factors that one stat or metric does not always mean exactly what it is purported to.

One example is defensive points allowed. It is sometimes called scoring defense in some books and categories. It is one number:  The points allowed by a team. However, it is not always the same as the points allowed by the defense. An offense can throw and interception and it is returned for a touchdown or lose a fumble that is returned for a score.

One game that highlights this is Green Bay Packers at Denver Broncos - October 15th, 1984. Denver jumped out to an early lead in a Monday Night Football game which they won 17-14.

Clearly the Packers defense only allowed three points but the "scoring defense" was recorded as 17 points.

The following chart takes away these pick 6's and sccop and scores and also ADDS IN the pick 6's and scoop and scores that the defense iteself has. It also takes away kick and punt returns and adds in safeties scored. We take the total of those scores and multiply by seven then add in 2 points for safeties.

This is a metric, not an exact calculation because sometimes an extra point can be missed or a tream can go for two points and be successful.

Yes, this does ignore interceptions or fumbles that occur deep into the opponent's side of the field that result in field goals. We are ignoring those because (A) it's too much work to find those and (B) this is just one metric that can be used along side others to determine effective defensive play.

Key: PA is points allowed. Non D points is the metric described above. Net PA is PA minus Non D Pts. We've included net yards allowed, sack percentage and defensive passer rating as well as total turnovers.
As can be seen Seattle still allowed the fewest points by their defense but they are essentially tied with the Chiefs. The Panthers allowed 308 points but the net total was about 252.

Though not perfect, it's a better gage than simple points allowed or using "scoring defense" to measure a defense's success.

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