But to have three rookies -- Johnson, Chicago's Matt Forte and Houston's Steve Slaton - surpass 1,000 yards before Week 15, and others (Carolina's Jonathan Stewart, Arizona's Tim Hightower, Baltimore's Ray Rice) lugging major carries for teams either already in the playoffs or fighting for a spot, is a faster return than anyone could have projected.
"We had a lot of guys that we really liked in the '08 draft," Reinfeldt said. "That hasn't been the case at running back in previous years."
Added Ravens GM Ozzie Newsome: "And a lot of these guys came out after their junior years. So this is a really talented group."
"This is a very talented group -- one of the most talented groups of running backs to come into the league and to contribute as fast as we have," Slaton said. "With so many guys doing so much so early, and some guys not even playing much because they're hurt or have been hurt, we're going to be contributing a lot to our teams for a long time."
Besides the talent, this class' football intelligence -- FBI in front-office vernacular -- is high enough for these players to transition from college, play and do everything that has been asked of them. So much so that their contributions are the reason why many of their teams still have something to play for with three weeks left in the regular season.
Johnson has 1,094 yards for the run-based Titans, who have already secured the AFC South title with the NFL's best record (13-1). Forte (1,081 yards, six touchdowns) is averaging 20 carries per game and has delivered nearly 37 percent of the Bears' offense. Stewart pulled to 699 yards with his 115-yard, two-touchdown showcase for the Panthers on Monday night against the Tampa Bay Buccaneers. Hightower supplanted veteran Edgerrin James for the NFC West-champion Arizona Cardinals.
But why has the group been so good, so fast?
Johnson, the fastest running back at the pre-draft combine, has eight runs of more than 20 yards and three of more than 40. Slaton has eight runs of more than 20 and four over 40. Stewart, who's perceived as more of a mauler, also has eight runs of more than 20 yards. Those three average at least 4.9 yards per carry. Forte is averaging 4.0 yards per run.
That's moving the chains.
Slaton, Johnson, Stewart and Forte all played in some version of the spread offense in college. The spread is predicated more on the quarterback making plays and getting running backs into space. That only works between the 20-yard lines in the NFL.
"It does make it tougher to evaluate them, just like wide receivers that play in the spread," Reinfeldt said. "Sometimes you have to figure out what they're seeing or reading and how that translates. It makes for a little bit more extrapolation."
Said Slaton: "We ran the spread (at West Virginia), but our running game was zone-based. What we do here is similar with the one-cut-and-go reads."
Said Newsome: "If a running back has certain skills, speed, vision, burst, he can cut, he can play in any system, whether it's the I-formation, offset or in a spread."
Johnson weighs 200 pounds, Forte 216 and Slaton 203. Detroit's Kevin Smith, who has 685 rushing yards, weighs 217. At 235 pounds, Stewart is the only prototypical running back in the group.
Forte and Smith were viewed as between-the-tackles workhorses, but Johnson, Slaton and Smith -- projected change-of-pace backs -- have shown interior ruggedness and the ability to break off big runs once they get to the second level of the defense, much like diminutive veteran Warrick Dunn.
"He's a much more complete back than what we thought," Reinfeldt said of Johnson. "He has the ability to pick up pass protection. He understands the offense, and he blocks. He kind of brings all the facets of a running back. We are very pleased."
Added Harris: "These guys are still rookies, though. You have to watch for things, and if they're not able to do certain things, you've got to take them out of those positions and put someone else in there who can handle things. There is still a huge learning curve."
Thousand-yard rushers Forte, Johnson and Slaton also are threats as pass catchers. Forte has 53 receptions for 495 yards and three touchdowns; Johnson has 39 catches for 257 yards and a score; and Slaton has 37 receptions for 290 yards and a touchdown.
"All those guys could play in space and catch the ball, which is why we liked all these guys," Harris said.
Nearly all of the thriving rookie running backs are part of a tandem on veteran-laden teams that have steady quarterback play and coaching-staff continuity. Those circumstances have eased the physical and mental workload and provided the support to offset the inconsistencies that arise among young players.
"If you have a pretty good football team, and you put a young guy like Chris Johnson in there, a guy that possesses great speed and he gets confidence that he's a good player, other guys are going to gravitate toward him to make sure he does the things he needs to do to be a good player," Harris said.
Said Reinfeldt: "There is less pressure on the individual when he's in that situation. It helps him become a more productive player."
Rookie of the Week?
Only Forte is the traditional bell-cow running back, averaging nearly 21 carries per game. Most of the others work in tandem, and none average more than 18 rushes per game.
"When you start doing things with tandem backs with a young player, it makes it that much easier because you can have certain parts of your playbook that allow you to focus on certain things with your young player, and you have certain things that work better with a veteran player," Reinfeldt said. "That's worked well for us."
Newsome agrees that the 2008 class is special, but he believes there should never be much surprise when a rookie running back emerges.
"Of all the positions, that's the easiest to make the transition from college to pro," Newsome said. "You're asking a guy to do the same things he did in Pee Wee, in high school and in college. If he has success running the ball at those levels, if he had vision and speed at those levels, you're not asking him to do much more. The blocking assignments can be difficult, but if he can run with the ball, that's what teams will have him do."