Measuring the Saints' game-by-game performance

Last week I tried to assess just how bad the NFC South was (extremely) and whether or not the Saints have a chance to turn things around (maybe). The latest division odds seem to bear that out, as the Saints are now favored to win the division for the first time since the season began.

This week, I’m going to explore the Saints’ week-by-week performance on offense and defense. While it seems apparent that the offense among the best and the defense is about as bad as the offense is good, those are just averages. The week-by-week numbers might tell us more.

So I measured the team’s performance in terms of Adjusted Yards per Attempt (aYPA). AYPA is a measure of offensive efficiency that is a strong predictor of winning. AYPA is an improvement on yards per attempt because it accounts for interceptions and sacks. There are a number of different ways of calculating aYPA, but my way is this:

[Passing Yards - sack yards - (60 * INTs)]/(passing attempts + # of sacks)

In English, you adjust the number of passing yards by subtracting the number of yards lost on sacks and take away an additional 60 yards per interception thrown. You then divide this by the number of attempts + the number of sacks, since sacks should count as passing attempts, too. Right now, the league average is 4.8 aYPA.

So here’s a graph of the Saints aYPA on offense and their aYPA allowed on defense. The color of the dot represents the point differential for the game: blue dots were wins and red dots were losses, with more intense colors indicating a more lopsided game. Also note that I reversed the y axis so that higher y-values means the Saints played better defense:

ypa

A few things jump out. First, the Saints’ passing offense has played above league average in every game but two: Cleveland (loss) and Tampa Bay (win). Second, note the three light red dots representing losses to Cleveland, Detroit, and Atlanta. Last week, I talked about how the Saints might have been slightly unlucky so far this year. These games are examples of that. Luck plays as much of a role in close games as skill does, and a team that wins a lot of close games in one year isn’t necessarily more likely to win a bunch of close games the next year. It’s fluky. That’s one of the reasons why teams that blowout other teams tend to be better than teams that eke out victories: blowing out teams is a sign of strength, eking out victories is a sign of luckiness.

Second, the Saints’ passing defense has been terrible, playing below average (often WELL below average) in every game but two. This is unsurprising, but sad. Just a little more defense vs. Atlanta, for example, and this season is looking much better. Of course, you could say the same thing about the offense and Cleveland, which was a more appalling loss in many ways. So it goes.

But that’s just passing offense. Here’s the same graph again, but using Advanced Football Analytics’ Expected Points Added(EPA) instead of aYPA. EPA is a more complete measure of offense and defense than just aYPA. Read the link for more details, but EPA essentially compares how the team does on every play vs. the league average for plays of similar down and distance and converts this into “Expected Points Added”. Higher numbers are better on offense and worse on defense, and the league average EPA per game is approximately 4.76.

[epa][12]

Note that some of the specifics are a little different, but the conclusions are the same: the Saints’ offense remains excellent, the defense remains decidedly unexcellent, and there are a couple of close games where a little better offense or defense would have made the difference.

[12]: http://www.whodatreport.com/wp-content/uploads/2014/10/epa.png