Last Sunday, Tennessee Titans running back Chris Johnson destroyed the Jacksonville Jaguars defense for 228 rushing yards on 24 carries -- 9.8 yards per carry, and a long run of 89 yards. An amazing 40 percent of the Titans' yards on the ground come after 10 yards this season, and that's just about all on Johnson, who leads the NFL in rushing with 824 yards. He also leads the league in big plays from a back -- 10 runs for over 20 yards and five runs for over 40. Once he gets past your front four, Johnson is a major problem to bring down -- especially when he's facing a team like the Jaguars, whose defense is emblematic of the NFL's current trouble with tackling. It seemed that every time Johnson hit the edge against the Jags, there was safety Reggie Nelson(notes), ready for another whiff. And Tennessee's underrated offensive line pushed Jacksonville's front four around all day.

However, Johnson's got a bigger challenge this week -- the days of "four-lane highway" rushing lanes and missed tackles might be over in the short term. The Titans face the San Francisco 49ers today, and this is a defense primed to stop the big play on the ground. They've only allowed three rushes of 20 yards or more, and no back has gone for 40 or more on them this season. San Francisco has speed on the perimeter and the ability to clamp down on speed backs. According to Football Outsiders, the Niners rank fourth in yards per carry allowed to the left end (2.52) and fifth in runs allowed to right end (2.42). Johnson will face additional challenges in that San Francisco's defense doesn't have much incentive to back into coverage with Vince Young(notes) under center. In fact, because Young rolls out so much, and is so much better as a passer when he does, the Niners have all the reason in the world to guard the edges above all else.

So watch San Francisco's edge defenders -- the always underrated Justin Smith(notes) at end, and outside linebackers Manny Lawson(notes) and Parys Haralson(notes) -- especially on those breakout plays in which Johnson tries to bounce outside. Last Sunday, the Niners negated Indy's rushing attack, and the ubiquitous stretch play, limiting Joseph Addai(notes) to 62 yards on 20 carries. True to the ethos of head coach Mike Singletary, these guys arrive at the ballcarrier in a very bad mood. Can they stop Johnson, the single most dangerous ground threat in the league?

Related: , Vince Young, Jacksonville Jaguars, San Francisco 49ers, Tennessee Titans