It is not always easy to see when an offensive lineman makes a true contribution to his team's success.
So-called "skill-position players" score touchdowns, while defensive stars can create turnovers or make bone-crushing, attention-grabbing hits. But those who carefully watch the play away from the ball know the "big uglies," as they are affectionately dubbed, can make a huge impact by simply doing their job -- whether by protecting the franchise quarterback behind them or creating holes for running backs to exploit.
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This year's draft includes a fair number of gifted tackles and a deep enough class of guards that there could be some long-time contributors available in the sixth and seventh rounds. Unfortunately, the same can't be said at center, where depth is lacking.
The following 10 linemen will be available at different tiers of the draft, but they all have a chance to be fixtures up front over the next seven or eight years -- making their impact by ensuring the household names around them can soar.
Thursday stars
Impact first-round offensive linemen are often in Pro Bowl contention due to their strong -- if not dominant -- run-blocking and reliable pass-protection skills.
Matt Kalil, OT, USC: Scouts do not consider Kalil to be quite in the elite Joe Thomas/Jonathan Ogden class as a left tackle prospect, but this 6-foot-7, 306-pound athlete should be among the best in the NFL at his position if he continues to mature physically and mentally with pro coaching. Bank on him making some trips to the Pro Bowl with his brother, Carolina Panthers center Ryan Kalil.
David DeCastro, OG/C, Stanford: Stanford fans have already seen how DeCastro consistently led the way for running backs by pulling around the tackle or stepping toward linebackers at the second level. That mobility and strength and his tenacity to stick on blocks make him a true impact run-blocker; he'll be coveted by teams looking to pound the ball in the run game.
Peter Konz, C/OG, Wisconsin: A willingness to slide to another position could be Konz's ticket to making an immediate impact in the NFL. If he ends up with the Baltimore Ravens, for example, as a late first-round pick, he could help a Super Bowl contender stay in the fight by starting at guard until veteran center Matt Birk is ready to hand over the reins.
Friday-night lights
Impact offensive linemen picked in Rounds 2 and 3 are often solid starters right out of the box, at times changing positions to fill in before veterans eventually depart.
Bobby Massie, OT, Mississippi: The highly recruited Massie has been the Rebels' starter at right tackle since mid-way through his freshman season, but some teams might give him a try at left tackle first, prompted by his long 35-inch arms and the athleticism he displayed against SEC pass rushers. He could actually end up going in the first round, if enough teams prefer his skills to those of Mike Adams (Ohio State) and Cordy Glenn (Georgia), but for now I'll consider him an impact pick on Friday night.
Jeff Allen, OT/OG, Illinois: A rising prospect in NFL circles, Allen was simply difficult to beat on the edge during his four years as a starter at both tackle spots. (He often played both sides in the same game over the past couple of seasons, as the Illini would flip the line based on the play call.) His build (6-3 7/8, 307) is more consistent with that of a guard, and he could transition inside if needed. Duane Brown, who was just one-quarter inch taller and eight pounds heavier than Allen when he was measured at the 2008 NFL Scouting Combine, was picked 26th overall by the Texans and has held down the tackle spot for the past four years. Allen has similar potential.
Kelechi Osemele, OG/OT, Iowa State: A mountain of a man (6-5 1/2, 333) with 35 7/8-inch arms, Osemele managed to consistently stop edge defenders during this three-year stint at left tackle for the Cyclones. His lack of lateral agility has turned off some scouts, but his pure power and surprising quickness off the snap should make him a force on the interior.
Saturday sleepers
Despite their long waits on draft day, impact offensive linemen selected in Rounds 4-7 often turn out to be long-term starters, especially at the interior positions.
Nate Potter, OT, Boise State: The 2011 first-team Associated Press All-American might have to wait until Saturday to be picked, due to his relatively svelte build (6-5 7/8, 303) and average strength. But he showed more agility (his times in both the short shuttle and three-cone drills ranked highly) and length (34 5/8-inch arms) than expected at the combine and should be a solid starter at left tackle with continued work in an NFL weight room.
David Molk, C, Michigan: Molk's smallish (6-1, 298) build won't allow him to fit in every NFL blocking system, but he did win the Rimington Trophy as the nation's top center in 2011. Relying on his mobility and functional strength (41 reps on the bench press at the combine), he should be able to excel for a decade in the NFL, like fellow small-but-feisty pivot men Casey Wiegmann and Todd McClure.
Lucas Nix, OG, Pittsburgh: Teams might hesitate to use an early pick on Nix because of a 2011 knee injury and an off-field incident after the season. But his size (6-5, 317) and strength in the run game stood out prior the injury. His experience at right tackle (16 starts in the 2009-10 season) gives him versatility that the other interior linemen that will be available on Saturday lack.
Follow Chad Reuter on Twitter @ChadReuter