When evaluating offensive linemen, it is important to consider all aspects of their games -- pass protection, run blocking, awareness and toughness.
Here's how we rank all draftable offensive linemen heading into the 2012 NFL combine by skill set (non-seniors noted with an asterisk). We also break down four-year measurement and timing trends, market trends at the position and 2011 Day 1 picks from the offensive line.
Pass protection
An offensive lineman needs good instincts to anticipate double-moves, twists, stunts and blitzes, and quick feet to get set in time. He has balance and body control in order to mirror and slide. He has lateral movement to shuffle back inside, long arms to keep separation and force pass-rushers wide, and a powerful punch to jar defenders and ruin their momentum.
Top three tackles
1. Matt Kalil, USC*
2. Riley Reiff, Iowa*
3. Mike Adams, Ohio State
Top three guards
1. David DeCastro, Stanford*
2. Cordy Glenn, Georgia
3. Markus Zusevics, Iowa
Top three centers
1. Ben Jones, Georgia
2. Mike Brewster, Ohio State
3. Quentin Saulsberry, Mississippi State
Run blocking
Size and strength are important in order to match up in the "phone booth." An offensive lineman needs to be nasty and aggressive and must possess adequate mobility to consistently get in position. He must take good first steps and angles on reach blocks. A wide frame allows tackles to engulf smaller defensive ends in the running game and a strong lower body allows them to finish off their blocks.
Top three tackles
1. Kalil
2. Jonathan Martin, Stanford*
3. Zebrie Sanders, Florida State
Top three guards
1. Glenn
2. DeCastro
3. Kevin Zeitler, Wisconsin
Top three centers
1. Peter Konz, Wisconsin
2. Jones
3. David Molk, Michigan
Awareness
An offensive lineman must be tactical. He needs to study film, learn tendencies and transfer knowledge to the field. He has to understand blocking angles and how to use technique in order to overcome physical deficiencies. He must be able to pick up new assignments quickly. Versatility -- the ability to fill in at multiple positions along the line -- can add to an offensive lineman's value.
Top three tackles
1. Martin
2. Sanders
3. Kalil
Top three guards
1. DeCastro
2. Joe Looney, Wake Forest
3. Zeitler
Top three centers
1. Konz
2. Molk
3. Philip Blake, Baylor
Toughness
Size and wingspan are important in order to engulf defenders at the point of attack. Also important is explosive upper-body strength to jar defenders with an initial punch and sustain blocks once locked on. An offensive lineman needs a wide base to anchor versus the bull rush in pass protection and strong legs to drive defenders off the line of scrimmage as a run-blocker.
Top three tackles
1. Kalil
2. Brandon Mosley, Auburn
3. Mitchell Schwartz, California
Top three guards
1. Glenn
2. Amini Silatolu, Midwestern State
3. Brandon Brooks, Miami (Ohio)
Top three centers
1. Jones
2. Brewster
3. Moe Petrus, Connecticut
Players who have draftable grades from Scouts Inc. buy were not invited to the combine: Adcock, Fisher, Harris, Brooks, Vlachos and Petrus.
Players who do not have draftable grades but received combine invites: Auburn OT A.J. Greene, Portland State OT Dustin Waldron and Southern Miss OT Lamar Holmes; Notre Dame G Taylor Dever, SMU G Josh Leribeus, Syracuse G Andrew Tiller, Memphis G Ronald Leary, Georgia G Justin Anderson, North Dakota State G Paul Cornick; Mississippi State C Quentin Saulsberry.
The following are graphic representations of the number of offensive linemen taken in the first two rounds of the 2011 draft, and the numbers selected in each round of the previous three drafts. Most teams use these kinds of charts to study position trends when setting up their draft boards each year.
Todd McShay is the director of college football scouting for Scouts Inc. He has been evaluating prospects for the NFL draft since 1998. Scouts Inc.'s Steve Muench and Kevin Weidl also contributed to this report.