The NFL Combine is the most important step in the NFL draft process for the majority of prospects, as hundreds of players travel to Indianapolis to be poked and prodded by 32 teams.

From official measurements to on-field agility drills to the medical examinations, the Combine puts each prospect in the same environment to evaluate them in a number of ways.

The 2015 Combine is scheduled for Feb. 17-23 at Lucas Oil Stadium in Indianapolis.

Sometimes referred to as the NFL Underwear Olympics, the Combine is an opportunity to match quantifiable data with a prospect’s scouting report, including everything from arm length to 40-yard dash time.

Even with more than 325 prospects invited this year, there were several notable omissions from the official list. Of the 84 underclassmen who declared early for the 2015 draft, 13 (15.5 percent) did not receive Combine invitations, including defensive end Deion Barnes and wide receivers Deontay Greenberry, Chris Harper and George Farmer.

Here is a breakdown of the snubs and surprises at each position:

QUARTERBACK

SNUB: Taylor Heinicke, Old Dominion

The face of the Old Dominion program the last four years, Heinicke was an integral part of the Monarchs moving to the FBS level last year. He doesn’t look like much, but he projects as a Chase Daniel-type of NFL prospect.

Other snubs: Chris Bonner (Colorado State-Pueblo), Hutson Mason (Georgia), Jake Waters (Kansas State), Bo Wallace (Mississippi), Taylor Kelly (Arizona State), Rakeem Cato (Marshall), Grand Hedrick (Boise State).

SURPRISE: Jerry Lovelocke, Prairie View A&M

Built well for the next level at 6 feet 4 and 245 pounds, Lovelocke has a lot of the physical traits that NFL scouts look for in a developmental prospect. His senior production was mediocre (16-9 TD-INT ratio and only 57.6 percent completions), but his skill-set has intrigued several around the league.

RUNNING BACK

SNUB: Malcolm Agnew, Southern Illinois

An Oregon State transfer, Agnew is a quick-footed runner with decisive burst to get north-south in a hurry and adds value as a pass catcher. He averaged 6.0 yards per carry as a senior, with 10 rushing touchdowns.

Other snubs: Dreamius Smith (West Virginia), Kevin Parks (Virginia), Terrell Watson (Azusa Pacific), Corey Grant (Auburn), Akeem Hunt (Purdue), Synjyn Davis (Georgia Tech), Venric Mark (West Texas A&M), Kenny Williams (Texas Tech).

SURPRISE: Gus Johnson, Stephen F. Austin

While he was certainly deserving of an invite, Johnson dominated in the Southland Conference, making him easy to overlook. He was among the nation’s leaders in 2014 with 1,683 rushing yards and 23 touchdowns, averaging 129.5 yards per game.

WIDE RECEIVER

SNUB: Deontay Greenberry, Houston

Despite abysmal blocking performances and dozens of drops on his collegiate résumé, Greenberry, who was a rare top recruit to end up at Houston, has the size/speed dimensions that NFL teams seek at the position.

Other snubs: Austin Hill (Arizona), Levi Norwood (Baylor), Jordan Taylor (Rice), Evan Spencer (Ohio State), Jaxon Shipley (Texas), Devin Gardner (Michigan), Matt Miller (Boise State), Chris Harper (California), Kasen Williams (Washington), Bud Sasser (Missouri), Jake Kumerow (WI-Whitewater), Nigel King (Kansas), Malcome Kennedy (Texas A&M), George Farmer (USC).

SURPRISE: Kaelin Clay, Utah

Although best known for fumbling the ball before crossing the end zone vs. Oregon, Clay has speed that could impress in Indianapolis. His size and unpolished routes aren’t ideal for the NFL, but standout times during speed drills could turn heads.

TIGHT END/FULLBACK

SNUB: C.J. Uzomah, Auburn

Although he wasn’t a central cog in Auburn’s offense, Uzomah was reliable when called upon, showing wide receiver skills with long arms to pluck. His struggles as a blocker showed at the Senior Bowl, but there is some promise there.

Other snubs: Casey Pierce (Kent State), Devin Mahina (BYU), Khari Lee (Bowie State), Gabe Holmes (Purdue), Connor Hamlett (Oregon State), Westlee Tonga (Utah), Brian Vogler (Alabama), Conner Neighbors (LSU), Hunter Joyer (Florida), Zach Zwinak (Penn State).

SURPRISE: Cameron Clear, Texas A&M

With only five catches in 11 games as a senior, Clear is easy to overlook, but NFL scouts think he was underutilized in College Station. Built well for the NFL game at 6-5 and 273 pounds, Clear is also more agile than his size suggests.

OFFENSIVE TACKLE

SNUB: Doniel Gambrell, Notre Dame College

A Division II standout, Gambrell, who has an inspiring backstory, played at a lower level, but he dominated the competition and has the skill-set for the next level. Combine or not, he’ll get a chance in the NFL.

Other snubs: Eric Lefeld (Cincinnati), Blaine Clausell (Mississippi State), Mickey Baucus (Arizona), Quinterrius Eatmon (South Florida), Jake Rodgers (Eastern Washington), Cameron Clemmons (Western Kentucky).

SURPRISE: Laurence Gibson, Virginia Tech

A part-time starter as a junior, Gibson started all 13 games at left tackle for the Hokies in 2014; and, although he needs technique work, he held up well on the edges, showing enough consistency to attract the attention of NFL scouts.

OFFENSIVE GUARD/CENTER

SNUB: Shaquille Mason, Georgia Tech

Arguably the most glaring snub regardless of position, Mason played guard in Georgia Tech’s triple-option offense, so it was tough to evaluate him. But he showed the balance, power and movements to lead some to believe he has NFL starter potential at center.

Other snubs: Miles Dieffenbach (Penn State), Ben Beckwith (Mississippi State), Kyle Costigan (Wisconsin), Shane McDermott (Miami), Leon Brown (Alabama), Brandon Vitable (Northwestern), David Andrews (Georgia), Matt Rotheram (Pittsburgh), Dillon Day (Mississippi State), Junior Salt (Utah), Kaleb Johnson (Rutgers), Chris Jasperse (Marshall), Quinton Spain (West Virginia), Malcolm Bunche (UCLA).

SURPRISE: Garrett Gramling, Texas A&M

Texas A&M has sent a number of offensive linemen to the NFL in recent years, but Gramling wasn’t on anyone’s radar entering the 2014 season. He started 10 games for the Aggies as a senior, showing versatility at both guard spots.

DEFENSIVE END

SNUB: Deion Barnes, Penn State

A junior who declared early, Barnes showed potential early in his career, but he struggled to show much improvement over the years and wasn’t able to show enough development to earn a Combine invitation.

Other snubs: Ray Drew (Georgia), Jermaruia Rasco (LSU), Shaq Riddick (West Virginia), Brock Hekking (Nevada), Marcus Rush (Michigan State), Ryan Mueller (Kansas State), James Rouse (Marshall), Cory Morrissey (Iowa State), Blake Lueders (Stanford), Mike Reilly (William & Mary), Brian Mihalik (Boston College), Andrew Hudson (Washington), Deiontre Mount (Louisville), Steve Miller (Ohio State).

SURPRISE: Frank Clark, Michigan

From a talent perspective, Clark has the physical traits to make an impact in the NFL and is worthy of showing off his skills in Indianapolis. But, after a domestic disturbance last November, he was dismissed from the Michigan program. He will have a chance to tell his story at the Combine.

DEFENSIVE TACKLE

SNUB: Xavier Williams, Northern Iowa

Although running back David Johnson is the notable UNI player in this class, Williams is a legitimate NFL prospect in his own right. His functional strength is a question mark, but he has active feet and the versatility to fit different schemes.

Other snubs: Kaleb Eulls (Mississippi State), James Castleman (Oklahoma State), Chucky Hunter (TCU), Travis Raciti (San Jose State), Darius Kilgo (Maryland), Warren Herring (Wisconsin), Brandon Ivory (Alabama), Jeffrey Whitaker (Auburn), Terry Williams (East Carolina).

SURPRISE: Leon Orr, Florida

Last November, Orr abruptly left the Gators’ program when he was upset over playing time, choosing to abandon his teammates before a game at Vanderbilt. He has the talent to compete in the NFL, but he had better be ready to answer the tough questions in Indianapolis.

LINEBACKER

SNUB: Junior Sylvestre, Toledo

Although he’s smallish for the position and played in the MAC, Sylvestre is a terrific athlete with speed who will test off the charts. However, he won’t get a chance to show off his wheels in Indy and will have to wait until his pro day.

Other snubs: Jeff Luc (Cincinnati), James Vaughters (Stanford), Derrick Malone (Oregon), A.J. Tarpley (Stanford), Zaire Anderson (Nebraska), Zach Vigil (Utah State), Houston Bates (Louisiana Tech), C.J. Olaniyan (Penn State), Dyshawn Davis (Syracuse), Terrance Plummer (UCF), David Mayo (Texas State), David Helton (Duke), John Timu (Washington), Curtis Grant (Ohio State), Norkeithus Otis (North Carolina), Quayshawn Nealy (Georgia Tech).

SURPRISE: Mark Nzeocha, Wyoming

Well-built at 6-3 and 239 pounds, Nzeocha flies around the field with range and speed in pursuit and was the best defensive player for the Cowboys. But a torn ACL last October ended his season and career at Wyoming.

CORNERBACK

SNUB: Cody Riggs, Notre Dame

After four seasons at Florida, Riggs was a graduate transfer for the Irish in 2014 and was the most consistent Notre Dame defensive back. He has the light footwork and toughness to fight for a nickel role as a rookie.

Other snubs: Deshazor Everett (Texas A&M), Imoan Claiborne (Northwestern State), Cam Thomas (Western Kentucky), Bernard Blake (Colorado State), Bryce Callahan (Rice), DeAnte Saunders (Tennessee State), Greg Henderson (Colorado), Merrill Noel (Wake Forest), Robertson Daniel (BYU), Tevin Mitchel (Arkansas), Raymon Taylor (Michigan), Nick Waisome (Florida State), Terell Floyd (Louisville).

SURPRISE: Tye Smith, Towson

Smith has been a prospect slowly creeping up draft boards, especially after a solid week at the East-West Shrine Game in St. Petersburg. He has earned his spot on the official Combine list.

SAFETY

SNUB: Erick Dargan, Oregon

At some point during the 2014 season, Dargan went from valuable contributor to dynamic playmaker for the Ducks, leading the Pac-12 in interceptions (7). He has his limitations in pass coverage but is a consistent performer with the ball in front of him.

Other snubs: Sam Carter (TCU), Dechane Durante (Northern Illinois), Brian Blechen (Utah), Damian Parms (Florida Atlantic), Tra’Mayne Bondurant (Arizona), Isaiah Johnson (Georgia Tech), Ronald Martin (LSU), Ryan Murphy (Oregon State), Serderius Bryant (Mississippi), Ray Vinopal (Pittsburgh), John Lowdermilk (Iowa), Nick Perry (Alabama), Robenson Therezie (Auburn), Austin Collinsworth (Notre Dame).

SURPRISE: Dean Marlowe, James Madison

A four-year starter at James Madison, Marlowe has experience playing near the line of scrimmage and in the deep half of the field; and, with a solid combine, he could earn himself draftable grades from teams.

Dane Brugler is an analyst for NFLDraftScout.com, a property of The Sports Xchange distributed in partnership with CBSSports.com.