It's not really fair to say that former Illinois defensive end Whitney Mercilus' 2011 season "came out of nowhere." It was the product of years and years of hard work on and off the field, and he wouldn't have gotten much attention from the Illini coaches if they didn't think he was capable of putting together a giant year.
That all said, if you're looking for on-field indicators that Mercilus was due for an All-American season, well, there wasn't much that separated Mercilus from dozens of other players. He managed just two starts in all of 2010, registering 16 tackles and three tackles for a loss.
He wasn't a particularly highly rated recruit—a couple other Big Ten offers but nothing big—and he wasn't projected onto any preseason 2011 All-Big Ten lists, not even Phil Steele's four-deep projections.
What ensued was pretty convincingly the best season for a defensive end in all of college football in 2011. Mercilus led all defensive linemen in tackles for loss (22.5), tackles for loss yardage (130 yards), sacks (16), sack yardage (105 yards) and forced fumbles (nine, including seven in Big Ten play). He earned the Hendricks Award for the nation's top defensive end and was named a consensus First Team All-American.
Mercilus was an absolute terror at the collegiate level, but he's going to have to find a role to thrive in as a pro, and at 6'3" and 261 pounds, that might take a little work.
He's been a defensive end in college the entire time, but he doesn't have the pure speed you'd want from an elite rush end. He also doesn't have the bulk to stand up a decent NFL-level offensive tackle on 3rd-and-short on any type of a regular basis, so playing three downs a series with one hand down seems like a bit of a fantasy in and of itself.
Fortunately, Mercilus looks like a quality fit as a rush OLB in the mold of a James Harrison in a 3-4 defense, provided that he works on zone responsibilities so he can't be schemed out of a play in one fell swoop (also, provided that he doesn't injure as many people around him as humanly possible, à la Harrison).
Make no mistake: Mercilus is a first-round-caliber prospect. He's strong enough to get a push on high-level tackles on the pass rush, and his hand-fighting and footwork allow him to disengage blocks and change angles to pursue the quarterback with frightening efficiency.
That's huge, because it can be the difference between a sack and a big play, either on a scramble or a deep pass. How many times, for example, did teams see their defensive end come flailing out of control at Tim Tebow, only to miss and break contain? That would be significantly less of a concern with Mercilus than your average defensive end, and that's why he would be a valuable addition to any 3-4 defensive front.