NFL: Top five rookies

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With eight weeks of the NFL season in the books, we examine which NFL rookies have made the biggest impact through the first half of 2015.

While most would say it takes at least two to three years to properly evaluate an NFL draft class, we can all agree that half a season is far too soon.

Nevertheless, that does not mean we cannot track which rookies have quickly made an impact for their teams and have positioned themselves to contend for coveted NFL Rookie of the Year honours at the end of the season.

1. Todd Gurley, RB (St. Louis Rams)

Draft slot: First round (10th overall)

Todd Gurley has started just four NFL games and already looks like the league's best running back. Over those four games, Gurley has rushed 566 yards which makes him the most prolific rusher over his first four starts since the AFL/NFL merger.

Through those four games, Gurley averages an absurd 141.5 yards rushing per game. Le'Veon Bell, prior to his season-ending knee injury, was second behind Gurley with 92.7 while Adrian Peterson is third with 90.4. Gurley's 6.1 yards per carry is joint first in the NFL alongside Ryan Matthews of the Philadelphia Eagles.

What makes Gurley's achievements all the more remarkable is the fact he is excelling with very little help. St Louis ranks dead last in the NFL in passing yards with 179.6 per game. Their inability to hurt teams through the air means defences are free to key on Gurley. To illustrate how difficult it is to thrive under these circumstances, consider Gurley's back-up Tre Mason (a 2014 third-round pick) is averaging just 2.7 yards per carry in relief of Gurley.

2. Amari Cooper, WR (Oakland Raiders)

Draft slot: First round (fourth overall)

Amari Cooper was hailed as one of the most pro-ready wide receivers to enter the draft in years when he declared after his junior season at Alabama and he has lived up to that billing through the first seven games of his NFL career.

Cooper's 80.7 receiving yards per game rank a very respectable 19th in the NFL this season. That is impressive given some of the tough match-ups he has faced – he was shadowed by Darrelle Revis of the New York Jets last Sunday and had to contend with Denver Broncos duo Chris Harris Jr. and Aqib Talib in Week 5. Outside of those two match-ups, Cooper has finished with 100 yards receiving or a touchdown in every game except the Raiders' opening-day blowout 13-33 loss to the Cincinnati Bengals.

Despite being just 21 years old, Cooper has already demonstrated the ability to be a difference maker at all three levels of the defence.

He put his full range of skills on display in Week 7 against the San Diego Chargers. First, he climbed the ladder to haul in a deep 44-yard pass from Derek Carr. Later in the game, he showed off his silky run-after-the-catch skills as he avoided numerous Chargers tacklers to take a screen pass 52 yards into the endzone (see video above).

3. Ronald Darby, CB (Buffalo Bills)

Draft Slot: Second round (50th overall)

Shutdown cornerbacks are an extremely valuable commodity in the NFL, and the Buffalo Bills may have hit the jackpot with their second-round pick Ronald Darby.

Entering Week 9 of the season, Darby leads the NFL with 14 passes defended and has also hauled in two interceptions to establish himself as a key player in Rex Ryan's defence.

Darby has been targeted 58 times through seven games but has yet to allow a touchdown pass. Opposing quarterbacks are completing just 48.3 per cent of passes into his coverage, and have a combined QB rating of 48.6 when targeting him.

Ryan's aggressive, blitz-heavy defence puts a lot of pressure on its cornerbacks to hold up in one-on-one coverage but in Darby and 2012 10th overall pick Stephon Gilmore, he has two who are more than up to the task.

4. Stefon Diggs, WR (Minnesota Vikings)

Draft slot: Fifth round (146th overall)

Stefon Diggs has exploded onto the scene as Teddy Bridgewater's number-one target in Minnesota, with 419 yards and two touchdowns in his first four NFL games.

His yardage total ranks Diggs second among all NFL players in their first four career games since 1960, landing him behind only Anquan Boldin's fast start from 2003. His overall totals compare favourably with last year's rookie wide receiver sensation Odell Beckham Jr, who managed 262 yards and three touchdowns in his first four NFL games.

Diggs was viewed as one of the best players in the nation and a consensus five-star recruit coming out of high school. He turned down scholarship offers from Florida, USC, Cal, Ohio State and Auburn, among others, to play close to home at the University of Maryland but things didn't go as hoped as he struggled with injuries throughout his time there.

Teams were unconvinced by Diggs' production (792 yards, five touchdowns in his final season) and allowed to slip into the fifth round but he is showing in the NFL he still has all the talent which made him one of the most coveted players in the nation coming out of high school.

5. Jameis Winston, QB (Tampa Bay Buccaneers)

Draft slot: First round (first overall)

Jameis Winston's NFL career got off to the worst possible start when the Tampa Bay Buccaneers were demolished at home by Marcus Mariota and the Tennessee Titans in Week 1, losing 14-42. Winston threw two picks in that game and was vastly outplayed by second overall pick Mariota.

Winston's performances have been a bit up and down throughout the season but he has always flashed the elite traits with made him the first player selected in the draft.

His decision-making has greatly improved as he has adjusted to the pace of the NFL. After throwing seven interceptions in his first four games (including four in a Week 4 loss to Carolina), Winston has not thrown any in his last three games. He has accounted for 12 total touchdowns, throwing for 10 and rushing for two more.

Tampa Bay managed to win just two games last season but have already won three in 2015 under Winston. The playoffs will be beyond their reach this season in a crowded NFC but wins in New Orleans and Atlanta against their NFC South division rivals the Saints and the Falcons will give them hope Winston is the right man to lead them forward.

Honourable mentions

Marcus Peters, CB (Kansas City Chiefs) – Has defended 11 passes (fourth most in the league) and hauled in three interceptions, one of which he returned for a touchdown.

Hau'oli Kikaha, OLB (New Orleans Saints) – The second-round pick has racked up four sacks and three forced fumbles so far for New Orleans and looks like a nice find.

Eric Kendricks, LB (Minnesota Vikings) – Leads all rookies in tackles with 42 and is tied with Kikaha for the lead in sacks with four.

Damarious Randall, CB (Green Bay Packers) – Has defended eight passes this season and intercepted Peyton Manning in the Packers' loss to Denver on Sunday.

Marcus Mariota, QB (Tennessee Titans) – The struggles of Zach Mettenburger highlight the lack of weapons in Tennessee and give you greater appreciation for Mariota's performances.