When asked if he has seen anyone faster than Titans rookie Chris Johnson, Steelers safety Troy Polamalu paused for a second and said, "I watched Usain Bolt this summer.
"Usain Bolt would run this guy down," he said, referring to the world-record sprinter.
Not many others.
Johnson, the leading rusher among all NFL rookies with 1,159 yards, is one-half of Tennessee's "Smash & Dash" tandem -- LenDale White is the other -- that has gained more yards than any other duo in the AFC. He also is the fastest running back the Steelers will face this season, a player who was timed at 4.24 at the NFL Scouting Combine.
Johnson is the Titans' home run hitter, a back with eight runs of 20 yards or longer, including three of 40 yards or longer. More impressive, he leads all NFL backs with 100 or more carries with a 4.9-yard average per attempt.
"He's one of the fastest guys I've ever seen since I've been playing, and that's just on tape," cornerback Bryant McFadden said. "It's a whole different vibe in person."
"When you have a guy who runs 4.2, when he finally gets a crack it's a touchdown," Steelers safety Ryan Clark said. "It's almost like watching Willie [Parker]. He runs, runs, runs and when he gets a crack, it's 40 yards."
That will be the top priority for the Steelers, who lead the NFL in total defense, are ranked No. 1 against the run in the AFC and have allowed fewer long runs than any other team in the league.
The Steelers have allowed just three runs longer than 20 yards this season, and only one longer than 40 -- a 41-yarder by New England's Kevin Faulk against their nickel defense. No other team has allowed fewer.
"With him, you can't allow him to hit a crease," McFadden said. "He hits a crease, he's not like any other back where guys can have an angle and go get him. He can just outrun the angle."
Why are the Steelers so efficient at preventing long runs?
Defensive coordinator Dick LeBeau said part of the reason is because all the members of the secondary are good tacklers. Also, Polamalu said the Steelers' two-gap style of defense, which requires the defensive linemen to "read" which way the play is going, forces a running back to move laterally and doesn't create as many gaps.
"When you're always two-gapping, you can never go downhill on the linebacker," Polamalu said. "Everything is forced to go laterally and, with the speed we have on defense, it's an advantage to us."
Either way, Clark, who is second on the team with 101 tackles, is ready for Johnson.
"I look at it like, the faster he runs, the more pad I get on him, the farther he's going to fly," Clark said. "Even a 4.2 slows up when you hit him enough."
Gerry Dulac can be reached at firstname.lastname@example.org .