This question came up in the comments for this week's PTN, and the answer required was a bit too lengthy for a response comment, so FanPost it is. The issue is as follows: conventional metrics have the Bulldog defense at 120th in the country in pass defense, which is Really Bad. Advanced metrics, namely defensive Passing S&P+, have CLANGA at 20th in the country, which is Pretty Darn Good. Somewhat of a disconnect, right?
My initial feeling is that this was due to garbage time adjustments (namely, that MSU's backups were giving up a bunch of yardage, dragging their overall numbers down). To figure this out, I pulled the box score for each of MSU's games this season, and did the usual garbage-time / success rate stuff on it. As a reminder, success rate is defined as attaining 70% of required yardage on first down, 50% on second down, and 100% on third and fourth downs, where required yardage is defined as the number of yards needed to make a first down. Garbage time is defined as plays that occur when the scoring margin is over 28 points in the first quarter, 24 points in the second, 21 points in the third, or 16 points in the fourth. Keeping all that in mind, this is what I found:
|Attempts||Yards||Yards per Attempt||Success Rate|
The game-by-game numbers are non-garbage only.
Oddly enough, nearly identical numbers in garbage and non-garbage time, on a per-attempt basis. So why are they rated so highly? Look at the passing S&P+ numbers of their opponents. Notice the lines corresponding to 1 (Auburn), 23 (LSU), and 25 (Texas A&M). Notice the comparatively small amount of yardage given up, the middling success rates, and the low yards per attempt numbers (LSU's 7.8 is not bad, but not exceptional for college either).
The success rate numbers really tell the story here, as they've averaged about 40% a game without much variance. South Alabama posted 47.6%, but on only 21 attempts for a measly 130 yards. MSU's allowed 7 pass plays of over 50 yards, and they happened to all come against Kentucky and UAB, the two worst yardage performances of the season. Over a sixth of their passing yardage allowed for the season came in those 7 plays.
So what does this tell us? On a per play basis, this team's pass defense is pretty solid. They've held effective offenses to well below their season average performances, and while they're maybe a bit susceptible to big plays, most have come against two opponents. One was a salty in-conference opponent on the road, another was a better-than-you-think mid-major the Bulldogs probably weren't taking seriously in the second game of the season.
In short, 20th may be a bit high for this group, but 120th is definitely way too low — and situations like this are why advanced metrics are just a lot more useful than traditional yards-per-game statistics.