I'd be intrigued to hear what others have to say, but I'm of the impression that the most important thing the 49ers need to accomplish this weekend is shutting down, or at least containing Titans running back Chris Johnson. If the 49ers can contain Johnson, the Titans will need to have Vince Young making plays. Of course maybe that makes Vinsanity the ultimate x-factor in this game. For now though, let's focus on Johnson.
Chris Johnson has obliterated any possibility of a sophomore slump as he is on pace to easily surpass his very impressive rookie season. Johnson currently leads the NFL with 824 yards, averaging a robust 6.9 yards per carry, and also leading the NFL with ten rushes of 20+ yards. Needless to say, Chris Johnson is rushing with a lot of confidence and is taking aim at 2,000 rushing yards. So there you have an irresistible force.
On the other side of the field, the 49ers roll out a rushing defense that leads the league in yards per carry allowed at 3.2. Often times this can be due to an abysmal pass defense. The 49ers pass defense has issues, but it's certainly not abysmal. Football Outsiders updated their unit rankings (Florida Danny will have more on that this week) and at this point, the 49ers rank third against the rush and 11th against the pass in terms of DVOA. So while the 49ers defense might not be #1 like Chris Johnson is #1, it is certainly turning into the proverbial immovable object.
So, as the classic question asks, what happens when the irresistible force meets the immovable object? Vince Young or Alex Smith could certainly go wild and be the difference-maker in this matchup. But I actually think this game comes down to who can win the matchup of Chris Johnson vs. 49ers rushing defense.
In looking at the matchup, it's certainly hard to bet against a guy like Johnson. I certainly don't doubt Chris Johnson's ability, but I also think some of his numbers can be questioned at least a little bit. For example, this past week he put up 228 yards...against the Jaguars. It's a great number, but it must be put in context. The two previous games he put up 128 yards in a 59-0 loss to the Patriots, and 34 yards in a 31-9 home loss to the Colts. The Patriots number is probably the most misleading given that it was 45-0 at the half. One might be able to infer that the Patriots were not exactly playing the toughest rush defense. I could be wrong, but when you lose by that matchup, I'm less inclined to be impressed by the numbers.
After the jump we look at the 49ers rush defense against quality running backs...
The 49ers rush defense has faced some solid running backs and done a fairly solid job for the most part. Here's a quick rundown of running back performances against the 49ers rush defense this season:
| Player | Carries | Yards | YPC | Long |
| B. Wells | 7 | 29 | 4.1 | 15 |
| T. Hightower | 8 | 15 | 1.9 | 6 |
| J. Forsett | 5 | 35 | 7 | 14 |
| J. Jones | 8 | 11 | 1.4 | 7 |
| A. Peterson | 19 | 85 | 4.5 | 35 |
| C. Taylor | 6 | 16 | 2.7 | 8 |
| S. Jackson | 23 | 79 | 3.4 | 15 |
| M. Turner | 22 | 97 | 4.4 | 33 |
| J. Norwood | 12 | 44 | 3.7 | 14 |
| S. Slaton | 18 | 67 | 3.7 | 31 |
| J. Addai | 20 | 62 | 3.1 | 13 |
This isn't exactly a scientific breakdown, but overall the 49ers have done a solid job in containing some quality running backs. Each player requires a bit of context, such as Michael Turner having three rushing touchdowns. However, if the 49ers can hold down Chris Johnson, I think things will be fine.
The 49ers certainly have the weapons and scheme on defense to do battle with Johnson. Obviously we know the players here. Patrick Willis, Michael Lewis, Aubrayo Franklin. Of course, the loss of Nate Clements will actually hurt a bit in the rush defense. Clements does a great job in open field tackles on running backs, so the team will have to overcome that. However, even without Clements, this is a swarming defense that is quick in attacking the ball-carrier.
So given all that, will the 49ers defense be able to take care of business this Sunday? Or do you think they can win even if Johnson runs wild? Feel free to throw out predictions on Johnson's performance if you'd like. Whatever his final yardage total, I think it will really come down to that yards per carry. If he's gashing the defense for 5 or 6 yards a carry, it could be a long day. But if he finishes with 100+ yards on 30+ carries, well then it's not as big a deal.