The Defensive Rookie of the Year Award is an arbitrary honor bestowed on a rookie who strings together a few "wow" performances during his first season. I say arbitrary because winning the award isn't exactly a guarantee of future success. Just ask Shawne Merriman. Still, it is a good indicator of who made an impression early on in their careers.

So, who is in contention for the award this year?

DT Aaron Donald, St. Louis Rams

Aaron Donald has more than lived up to his first-round expectations this season. Donald has recorded 8.09 sacks when lined up as an interior lineman this season. That number trails only Gerald MCCoy (8.5) and Ndamukong Suh (10.0) for the most ever in a player's first season.

In 388 dropbacks with Donald on the field, opposing quarterbacks have a total quarterback rating of just 44. The Rams are ranked 11th in pass defense and 12th against the run largely thanks to the disruption Donald has caused in opposing backfields.

ILB C.J. Mosley, Baltimore Ravens

Mosley has outperformed most seasoned veterans this season, let alone the rookie class of defenders. Among linebackers this year, Mosley is fifth in total snaps (877), seventh in tackles (117) and second in interceptions (two). All of those numbers either lead rookie linebackers or are tied for first.

Most importantly, Mosley has been making game-changing plays. He is one of just three rookies (the others being Bradley Roby and Telvin Smith) to record at least one sack, interception, forced fumble and fumble recovery this year.

OLB Khalil Mack, Oakland Raiders

Oakland's poor season has largely overshadowed Mack's impressive first year in the NFL.

The No. 5 overall pick has made a difference on what was one of the league's worst defenses last season. The Raiders rate above average in defensive efficiency against the run and yards per rush this season. They have caused a league high 69 negative rushes this season.

Individually, Mack has 27 tackles for a loss or no gain, ranking first among rookies and sixth overall for defensive players. The guy just flies to the ball.

Honorable Mentions

ILB Chris Borland, San Francisco 49ers

OLB Anthony Barr, Minnesota Vikings