COLUMBIA — When college football recruits sign their letters of intent on Wednesday, South Carolina will secure probably its best group of offensive linemen in coach Steve Spurrier’s nine recruiting classes.

But will they become productive players? Regardless of how positive a coach spins at his press conference, that is the unanswerable question on every National Signing Day. Recruiting is an inexact science, and perhaps no position is tougher to evaluate than offensive line.

It is obviously critical for any offense that wants to succeed, especially in the Southeastern Conference, where fearsome defensive lines are the norm.

Under Spurrier, USC has had uneven results in offensive line recruiting.

Partly because of this, the Gamecocks’ offense has sputtered at times. While they finished 11-2 in 2011 and 2012, they ranked 73rd and 84th nationally in yards per game. They allowed 30 sacks in 2011 and 38 last season, No. 85 and 110 nationally.

There are mitigating factors. USC’s best offensive player, running back Marcus Lattimore, missed 10 combined games the past two seasons because of knee injuries. And it is shortsighted to blame an offensive line for every sack allowed

Still, Spurrier made no secret last season about his frustration with his line’s inconsistent performances, though the group improved later in the year.

Spurrier has two highly rated linemen in this class – Maryland’s Na’Ty Rodgers and Dillon High’s D.J. Park, who are rated the No. 15 and 19 tackles by, and the No. 181 and 220 overall recruits. Bryce King, Park’s high school teammate, is rated the No. 3 center.

Two of USC’s recent top line recruits have worked out reasonably well so far. Goose Creek’s Brandon Shell started as a redshirt freshman right tackle last season. He was the No. 4 tackle and No. 66 overall recruit in 2011.

A.J. Cann last year was a third-year sophomore in his second season starting at left guard, after being the No. 2 center and No. 182 overall recruit in 2010.

But for every Shell and Cann, there are players like Quintin Richardson, the No. 8 tackle in 2007, who never significantly contributed in three seasons and transferred to lower-division Hampton. Or Tramell Williams, the No. 9 center in 2010, who redshirted that year, then transferred. Or Kevin Young, the No. 20 tackle in 2006, plagued by injuries at USC and never a factor.

USC isn’t alone. Just look at Rivals’ offensive tackle rankings in 2007. The top three are Josh Oglesby (Wisconsin), Ryan Miller (Colorado) and Matt Romine (Notre Dame). Ever heard of them? Probably not. They had uneventful college careers, for various reasons.

But at No. 6 is Bryan Bulaga (Iowa), a first-round pick by the Green Bay Packers in 2010 – a testament to the riches available if you prove you can play this valuable position as well as everybody thought you could when you were 18 years old.

Size, smarts not guaranteed

That is a substantial “if” for several reasons. Certainly, the high potential for injuries on the line, where collisions are the closest and most frequent, makes it difficult to project long-term success out of high school. There are other factors, such as physical growth, mental acumen and the willingness to embrace a thankless existence of physical punishment.

“Offensive linemen are the hardest guys, I think, to evaluate,” said Goose Creek coach Chuck Reedy, a former longtime college assistant coach, including 1978-89 at Clemson. “There are a lot of intangibles that make them more difficult to evaluate than other positions.”

Before college assistants worry about whether a kid is smart enough to play offensive line in the SEC, they must consider one thing above all else – size. Few linemen emerge from high school large enough, which is why most redshirt. College coaches have to look at a kid and determine whether he can pack on 30 pounds, keep it on during the season and still move nimbly.

“It’s the hardest position to figure because you can’t really tell what their developmental process is,” said Dillon coach Jackie Hayes. “You’ll see a lot of big kids that play, but their coordination is not where it needs to be. Sometimes, you go out on a limb, and hopefully you can develop that.”

Shell, who is 6-6, now weighs 330 pounds. In the fall of 2010, as a high school senior, he was 290. Reedy said Shell’s frame indicated he could add weight. But high school tackles who are 6-4 and 270 pounds “are the ones that sometimes you have a hard time projecting,” Reedy said.

Everyone knows you need more than size to play college offensive line. High schools use about three to four blocking schemes, half as many as colleges, said Hayes.

Defensive fronts are more complex and disguised in college, so “you’ve got to be able to instinctively react to what you’re seeing,” Reedy said.

College coaches usually gauge a recruit’s intelligence by asking about his grades. But Goose Creek and other high schools around the state are now using a computer program that could help recruiters better determine a kid’s commitment to learning football. It’s called Hudl, and it lets players access their team’s film database from home. Coaches can see when players log in, so they know who is putting in extra work.

The tell-tale sign of potential?

Even if a recruiter knows a lineman is big and watches film, analyzing his games can be difficult. Many high schools, like Goose Creek, still use run-focused offenses that require little pass blocking. The spread offense is becoming more popular at places like Dillon, but because it uses quick passes, a tackle doesn’t have to hold off a defensive end for long. And of an elite lineman’s hours of game action, many are against defensive linemen who are much lighter.

“You don’t get to see them display their skills the way you do skill (position) guys,” Reedy said. “A skill player, you’re going to see their speed. You’re going to see them catch the ball. If it’s a defensive guy, you’re going to see how loose their hips are, how they backpedal. A quarterback, you can see him throw. A lot of times, the level of competition doesn’t factor in with those (skill) guys because the skills they have are the skills they have.”

Mike Farrell, Rivals’ national recruiting analyst, believes there is one trait that shows up on an offensive lineman’s game film, regardless of the system or opponent. And it is a must-have in college – aggression. For that reason, Farrell doesn’t find offensive linemen as difficult to analyze as cornerbacks, because they never get thrown at, and quarterbacks, because so much of that position is mental.

Farrell still remembers the film of guard Andre Smith, who went to Alabama and was the sixth overall pick in 2009. Smith had a sloppy-looking body, but Rivals rated him the No. 2 overall recruit in 2006 largely because of what Farrell noticed about Smith’s attitude.

“This kid was blocking kids into the first row,” Farrell said. “And you’re like, ‘Oh, my gosh, this kid’s an animal. He’s going to be super successful. He just wants to put you in the bleachers.’ That’s the only way you can tell if a kid has it or doesn’t: How does he respond to getting popped in the face?

“I don’t care who you’re playing against. As long as you put him on his butt every play, that shows me something. I think physicality comes out on film pretty quickly, and I think it’s the most important factor by far, especially with these freaks on the defensive line. You better be willing to hit that guy as hard as you can.”

For that reason, Farrell is hopeful about Rodgers, USC’s top-rated tackle for 2013. Yes, Rodgers tends to hold defensive ends, a flaw USC’s coaches can fix, Farrell said. But he will come to Columbia with something that is harder to teach, something Farrell saw at a camp when Rodgers was knocked down and had his lip bloodied, only to come back and play angrier than before.

“He’s a kid they don’t really have to worry about, the first time he gets hit, going home and crying,” Farrell said.