COLUMBIA — In the months leading up to the NFL draft, Mel Kiper Jr. watches hundreds of hours of game video. Analyzing and rating the best prospects available every year is far from an exact science, even for those employed by NFL teams. But all of them — scouts and Kiper alike — try as hard as they can to offer a precise assessment.

Before this year’s draft, Kiper said there was one offensive player who he had the most trouble evaluating during those hours of film viewing. The kid has prodigious talent, but also lots of questions about his physique and work ethic.

That player: South Carolina wide receiver Alshon Jeffery.

As a sophomore in 2010, Jeffery played well enough to put himself on track to being a first-round pick this year. He left school early after last season as one of the best receivers in school history. But nobody expected him to get picked in the first round, and indeed he wasn’t, as the Chicago Bears selected with the second round’s 13th pick Friday night.

Jeffery was the second player from a South Carolina college selected Friday, behind Clemson defensive end Andre Branch, who went sixth in the second round, to the Jacksonville Jaguars.

Jeffery was the seventh receiver picked in this draft, and now it is up to him to prove he deserved to go higher. But for Friday night, the conversation focused on why he fell behind those other receivers, including second-round selections Brian Quick of Appalachian State and Stephen Hill of Georgia Tech, who was picked by the New York Jets, two spots ahead of Jeffery.

Weight has long been a concern for Jeffery. He is 6-3 and played last season around 230 pounds. He dropped to 213 for USC’s pro day last month, at which he ran his 40-yard dash in about 4.5 seconds, according to ESPN draft analyst Kevin Weidl. Official times were not released.

That reported time was a positive sign for Jeffery, whose size is a greater asset than his speed. In three college seasons, Jeffery set USC’s record for career receiving yards (3,042) and tied the record for most career receiving touchdowns (23). He ranks second with 183 career catches. He also had 12 career 100-yard receiving games, another school record.

But college stats matter only so much when projecting professional achievements. And neither the numbers nor Jeffery’s 40 time at pro day dispelled all the questions, as opinions about him remained sharply divided.

One NFL scout told the Milwaukee Journal-Sentinel that Jeffery has “the best downfield ball-snatching ability of any receiver in this draft.”

Another scout had less flattering things to say to the newspaper.

“He thinks he’s entitled,” the scout said. “I don’t think he has a driving passion for the game. He plays the game really hard but he doesn’t do anything else hard. I don’t think he trains well. He’s soft.”

A third scout told the paper, “You’ve got to get the kid to buy into your program. There’s risk there, but there’s a huge reward, too.”

Kiper’s primary uncertainties about Jeffery involve his physique.

“The biggest problem with Jeffery is you don’t know what his body type is going to be,” Kiper said. “The weight that Alshon Jeffery tested at is not the weight that he played at. So what’s he going to play at? What’s his best playing weight going to be? Can he be strong enough at a lower weight? If he gets his weight up, is he going to separate enough? Is he going to be able to get open?”

People are also asking a lot of questions, and talking high risk/reward, about another big Chicago receiver, 6-4 Brandon Marshall, who the Bears traded for last month.

Marshall is obviously more proven than Jeffery, with 6,247 yards and 34 touchdowns in six seasons. But when they meet soon, perhaps Marshall will talk to Jeffery about how he responded to being passed over. In 2006, Marshall was a fourth-round pick.