We're in Week 4 of SB Nation's Rookie Watch, a series meant to track and analyze rookie player performances throughout the season. The jump from college football to the NFL is difficult, and rookies have to learn new schemes, new systems, figure out new coaches, new teammates and play against bigger, faster and better opponents across the board. Players that stand out early in their careers are doing so against the odds.

Last week, I talked about about rookie receivers that were making an early impact for their respective teams, and this week let's take a look at some running backs that hit the ground ... running.

Most people didn't expect to see much of Jerick McKinnon in his first season, but the third-round pick out of Georgia Southern was pushed into action, for obvious reasons. Backing up Matt Asiata this week against the Falcons, McKinnon carried 18 times for 135 yards, including this 55-yard scamper that took the Vikings out of the shadow of their own goal-line in the second quarter.

McKinnon's speed and explosiveness are apparent here, and his overall athleticism, combined with progress in pass protection, could mean he's in line for more carries this year. McKinnon is one of the most absurdly athletic specimens of the last five years -- at the Scouting Combine, he ran the 40 in 4.37 seconds while registering a 40.5" vertical jump and an 11-foot broad jump. That's explosiveness, and even more importantly, it shows up on the field.

Below, you can see him hit the crease quickly behind some excellent blocking, then kick it into low gear to break through several arm tackle attempts.





McKinnon's big game actually shoots him to third on the list of rookie running backs for yardage this season (142 yards), behind Terrance West, whose Browns had a bye this week, and Lorenzo Taliaferro. Hey, what a great segue to Taliaferro.

Lorenzo Taliferro, Ravens

The Ravens picked the 6', 225-pound Taliaferro in the fourth round this year out of small-school Coastal Carolina. With the release of Ray Rice, the Ravens have turned to him to contribute early on. In a time share with Bernard Pierce and veteran Justin Forsett, Taliferro, despite his somewhat rigid running style, looks to be a great fit in Gary Kubiak's zone blocking scheme. These types of decisive big backs commonly work well in the ZBS because it's conducive to a 'one-cut' downhill style.

Below you can see him see his cut back, attack the hole with a gusto, then make a few more assertive cuts before breaking a tackle or two for big yardage.





Taliaferro rushed 15 times for 58 yards and a touchdown against the Panthers this week, and now sits at 33 carries for 149 yards and two scores on the year. He's averaging 4.5 yards per carry.

Williams was absurdly productive at Boston College, and the Giants drafted him on the fourth round to act as an understudy to Rashad Jennings. He's a big back at 5'11, 234 pounds, but moves well and has an explosive burst element to his game. Importantly, he's a sustainer -- he has shown he can weather a full season of carries -- and he's strong when tackled, falling forward instead of getting stood up.

Against Washington on Thursday Night, Williams got 15 carries for 66 yards and a goal-line touchdown (which he powered forward and through the plane to score after getting hit). This run from the third quarter demonstrates his agility well.

Speaking of agility, there weren't many running backs in this year's draft with more lateral explosiveness than Sankey. The rookie out of Washington got some garbage time action in a blowout loss to the Colts on Sunday, but showed why many in Tennessee are excited to see him get more carries going forward.

Below, you like his cutback when he sees the Colts safety crashing down toward the sideline, and the speed at which he gets downhill, but you'd like to see him keep his feet under him.





The very next play, for instance, he demonstrates some of that burst that made him a second-round pick.





Sankey is averaging 5.1 yards per carry thus far, but is in a secondary role. In his four games, he's carried the ball six times, two times, 10 times and six times again. With the Titans struggling on offense thus far this season, perhaps he's a spark they could use?

Honorable mentions:

The Browns' rookie backfield duo of West and Isaiah Crowell would have likely made this list if not for a bye this week, and there are a few other rookie running backs making an impact for their respective teams. The Texans have called on LSU rookie Alfred Blue to fill in for an injured Arian Foster, and he has 127 yards on 34 carries for Houston. Jeremy Hill has 26 carries for 126 yards in three games for the Bengals, but they too had a bye this week. Carlos Hyde has looked good for the Niners thus far, and Ka'Deem Carey got a little action in garbage time for the Bears this week against the Packers.