There are lots of things to look at when evaluating a running back, and environment is certainly one of them. Backs with better lines will produce more yardage per carry. Simple. What is not simple (or particularly easy for a fan to do) is evaluate what kind of fronts they are facing. It is a common notion that the "elite backs", think the AP's and the Jamal Charles', routinely face 8 men in the box, made worse because few respect their QBs.
Let's look back then, and delve into this notion. For the Titans, we are of course discussing CJ's struggles in relation to who the Titans have at QB, namely Jake Locker (mentioned way more than Fitz in the CJ apologist arguments). I suppose it's best to look at the best season from the best back to get the results we're looking for, since they will be inflated and trends will be easier to delineate.
In 2012, Adrian Peterson was no doubt the best RB in the NFL. He broke the 2000 yard mark, yada yada. So what did he face that year in terms of defensive fronts? Consider that he had Christian Ponder behind him all year, who was averaging less per completion than the Vikings were averaging on the ground...it doesn't get more lopsided than that. DC's did not lose sleep over Ponder, let's leave it at that. When pulling up the numbers, AP faced 8 men in the box less than 30% of the time. That's it, less than 1/3 of every play he was on the field.
It is an easy indicator for DC's, that a run is likely in certain situations: 3rd and short, goal-line, and when the offense splits only a single WR wide. This invites eight man boxes. The Vikings ran out of this formation more than most that year, splitting a WR out often when they decided to run the ball, opting for an additional blocker to counter the extra man. The results speak for themselves.
NFL running backs face 8 man fronts on an average of 23.3% of plays. That means, despite insinuation that the best NFL backs routinely face 8 in the box is false, and using the QB as an excuse for that is even more erroneous. That may well have been the case in the 90's, but the assertion doesn't hold water today, and it's not close. The NFL is ever changing, and the days of being able to stack the box consistently and hope to survive the aerial assault are long gone. It's simply not a realistic strategy to stack the box on lots of plays, which is why you see it no more than 30% of the time, even against top backs.
CJ faced essentially the same kind of fronts other RBs in the league faced, and even less than the top performers, so it is unfair to pin that as the reason for his struggles. The offensive line has plenty of blame in the matter, and the Dowell Loggains, for all his issues, did use Collin Mooney and especially Delanie Walker to counter the 8 in the box when it was there. But after all the research and the film study, it is clear to me that, there is little correlation between number of 8 man fronts a given RB faces and QB quality. Sure, logical rules will always apply but DC's in this league know that even the most mundane of quarterbacks at the NFL level are capable of shredding undermanned defenses, and that trend is only increasing. In fact, the numbers (and several notable playoff situations last season) show that coaches are becoming less "brave" in the way they roll out stacked boxes, even against the best NFL backs on short yardage situations. With the amount of weapons on the field and the way offenses are using TEs and receivers, that is no surprise.
Nowadays, the defense is characterized more by the inclusion or not of a nickel corner. The rise of the position's importance has stemmed from the need to defend the slew of slot specialists that have been dicing up NFL defenses on an increasing scale the past few years; Cruz, Welker, Wright, etc. These guys need to be able to come into the box and tackle in the run game, and they need to be quick enough to keep pace underneath, with the speed to cover should the slot man go deep. It may as well be a different position these days, and I think it will go that direction in the near future.
So we can officially leave Locker, Alex Smith, and just about any other QB out of the debate when it comes to the struggles of running backs facing 8 man boxes. The numbers don't back it up in the slightest. And for the record, let's stop comparing CJ's stats next to Eddie George's, and even backs from earlier times in the NFL. 2014 is not 1999.