As the knowledge of sabermetrics continues to cascade into other sports, it is often met by resistance. Sometimes, it's because of people who'd rather you do something along the lines of leaving your mom's basement and watching the game. But other times, it's because of a reason that actually makes logical sense.
Baseball is one of the easiest sports to contextualize. There's a batter, there's a pitcher, there's a pitch, and then it's over. Yes, there are other parts of the game that come into play, but for the most part, all of the action in the game takes place between two players and it's extremely easy to figure out what happened and why. In football, however, you have eleven working pieces on each side. Sometimes these players cover a player one-on-one, sometimes they don't. Sometimes the players blitz, sometimes they don't. Sometimes a great receiver is paired with a terrible quarterback, and sometimes a player that doesn't have much talent is a perfect fit in a system that makes the best of what he has.
To cut a meandering story short: statistically, the Texans pass defense is absymal. But when the Texans opponent's throw the ball at Kareem Jackson, they aren't getting much better results than they would if they targeted any other player on the Texans. Nobody who has watched a game of Texans football this year would claim that Jackson is good. Nobody who knows the inner workings of the Texans defense would claim that Jackson is a valuable player. In fact, most would say that if it was all about play, he should be benched. But statistically speaking, the Texans aren't much worse off when teams throw at him.
Look at Football Outsiders' DVOA for the Texans defense, and you'll see a pass defense that (through Week 8) is the second-worst in football. But look at the splits, and you'll notice that against #1 WR's, other WR's, TE's, and RB's, the Texans defense is 6.6% or more worse than average against all of them. Against #2 WR's,which are the ones that Jackson has usually been matched with, the Texans are 25.8% worse, a figure which is 28th in the league. A far cry from good, for sure, but much better than their ranking against tight ends and not far from their rating against running backs. So Jackson isn't good, but statistically, you can see that he's just a bad cog in a bad defense.
Now, lets look at his splits in FO's game charting project. I run the Texans part of the project, meaning it's my job to watch every Texans game through a magnifying glass and see who was thrown at, who was blitzing, and all of that fun jazz. Lets compare the splits of Jackson as the primary defender on a pass play to the other members of the Texans back 7. All stats are through Week 8's game, so we don't get to add in the two torchings that the Chargers gave Jackson just yet.
You can see that Jackson is hardly a standout in any area other than giving up copious amounts of yards after the catch. Bernard Pollard has allowed more touchdowns, and he has the lowest completion rate on the team outside of Eugene Wilson. Zac Diles' numbers look tremendously awful.
But the thing is, when you strip something of it's context so thoroughly, you can create just about any story you want.
Yes, Diles and Pollard aren't good in coverage. They never have been. Pollard was never really close to being good, despite the interceptions last year, and Diles has been about average the last few years. However, the football viewers tale is that Kareem Jackson has been beaten deep so often (see the YAC) that he was benched in a few games. Diles and Pollard may not be good, but they aren't this bad either. Frank Bush's schematic adjustment to how bad the pass defense was deep went as follows: play more deep zones and give Jackson safety help when possible.
Because Wilson, who you can see has hardly been matched up one-on-one with anyone this season, is so busy giving extra help to Jackson, the targets of the other defenders in coverage go up. When the pass rush can't get there, the extra targets go to Pollard's men. When the pass rush can get there, the balls go to Diles' men. When a ball is thrown at Jackson's man, it's often forced into a tighter spot due to the safety coverage, or thrown over the top where you will generally get more incompletions. And well, you can see how that works out for everyone involved. It's a cascade effect of badness, with Jackson as the focal point.
So while statistically speaking, you might even say a throw to Jackson is a good outcome for the Texans defense based on the completion percentage. You can't look at an eleven player game in a one-on-one context as you would in baseball. Statistics like these do not tell the full story of what Jackson has done to the defense. That isn't a strike against statistics, it's a strike against the scope you use them in. Football statistics need to be handled like a Fabergé egg. Trying to separate one player's contributions from the rest is a process that can't be left to just statistics, nor one that can be left to just observation. It takes a complete deductive process to figure out that Kareem Jackson is problem number one in the Texans secondary. He's certainly not the only problem, as you can see, but he's definitely the biggest one.