EVANSTON, Ill. -- Northwestern running back Venric Mark doesn't need a doctor to make the diagnosis.

Like most things in his life, he can do it all by himself.

"I have little man's syndrome," Mark told ESPN.com. "I've had that all my life, since Day 1. I've always been the small guy in the group. I've always been the guy that people go, 'Oh, no, let's not pick him.' So in my head, I'm thinking, 'OK, you're not going to pick me. I'm going to show you why you should have.'"

Any college coach who wouldn't pick Mark after the first half of the 2012 season hasn't been paying attention.

Mark might be 5-foot-8 and 175 pounds, but he's the single biggest reason why Northwestern sits at 6-1, right in the thick of the Legends division race. Along with Iowa running back Mark Weisman and Penn State wide receiver Allen Robinson, Mark has been one of the Big Ten's surprise offensive stars through the first seven weeks, rushing for 792 yards and eight touchdowns.

He ranks fifth in the league and 15th nationally in rushing average (113.9 ypg). He also leads the league and ranks fourth nationally in all-purpose yards (184.6 ypg), recording two punt returns for touchdowns and 15 receptions, one for a touchdown. After putting himself in position to break most of Northwestern's career return records, Mark's emergence at running back has put the team's all-time career all-purpose yards mark (5,271 by Damien Anderson) very much in play.

"He's just playing at a high level right now," Northwestern coach Pat Fitzgerald said. "... He's a joy to coach."

Northwestern had 1,000-yard rushers every season from 2002-06, but none since. The team has lacked a true threat at running back since Tyrell Sutton departed after the 2008 season. For an offense born out of the Rich Rodriguez-style spread, it was a problem.

Few would have pegged Mark, a return specialist who struggled to find a true position for two years, to be the answer. Just don't tell him that.

"He has a level of intensity that if he was Muhammad Ali, he'd be knocking everybody out," said Northwestern linebackers coach Randy Bates, who recruited Mark out of Houston's St. Pius X High School.

Several times after runs, Mark has confronted defenders more than a half-foot taller than him.

"With football, emotions run high, people talk," Mark said. "For me, that's fuel. When they say, 'You ain't getting this,' that just motivates me."

Mark's edginess is his defining trait, even more so than the top-level speed that got him on the field at Northwestern as a returner and has been showcased on long runs, like scoring bursts of 48 and 26 yards last week against Minnesota. He's not a scat back who spends all his time on the perimeter.

He's a between-the-tackles runner who, along with quarterback Kain Colter, has boosted Northwestern's red zone run game, a weakness of the offense in previous years.

"Inside zone is his favorite play," Northwestern running backs coach Matt MacPherson said. "You have to be a special kid, a tough kid, and Venric is pound-for-pound one of the toughest guys on our team. He embraces that role. He wants it."

McPherson likened Mark to former Northern Illinois star Garrett Wolfe, who checked in at 5-7 and 185 pounds and while displaying tremendous speed in space, also had success between the tackles. Wolfe led the nation in rushing (1,928) in 2006.

When Bates began recruiting Mark, he heard some doubts about whether Mark could play in the Big Ten because of his size. Mark won Bates over with his intensity, a quality they share ("We're both pretty whacked-out in our own way," Bates joked).

The question always seemed to be where Mark would play.

Special teams was a given, and Mark became Northwestern's primary returner as a true freshman in 2010, averaging 26.2 yards on kick returns with a touchdown, and 12.9 yards on punt returns. He also stood out on kick coverage.

"There's no doubt in my mind if ever played anywhere at the next level, he could be on all special teams," Bates said. "He was a punt gunner and he was a kickoff guy, and obviously great returning. All that special teams value, even if he never played a snap on offense or defense, he already was a good player."

The coaches tried Mark at slot receiver, but he had just six receptions in his first two seasons, playing behind All-Big Ten selection Jeremy Ebert. There was some talk of using him on defense, but it never materialized. Although Mark came to Northwestern with the idea of simply being the team's starting returner, he wanted more and wasn't happy at receiver.

"I wanted the ball," he said. "I'm that type of player, I'm not going to lie to you. I like having the ball in my hands."

The coaches moved Mark from receiver to running back midway through the 2011 season.

"We weren't quite sure what position we were going to start him at, and as you can see, we were wrong," Fitzgerald said. "Hindsight being 20-20, we wish he would have started in the backfield sooner."

MacPherson knew Mark could make plays in space. His concern was how Mark would handle the mental challenge of being a running back in the Big Ten, where "you get the crap beat out of you," while remaining effective as a receiver and a blocker in Northwestern's offense.

Offensive coordinator Mick McCall wants to get Mark 25 touches per game. While MacPherson admits those won't be 25 inside zone plays, Mark has shown he can be a featured back, despite his size.

"I can take licks," Mark said. "Being a running back, you're going to get bumps and bruises. But it's how you play with them, it's your mindset. Coach MacPherson always talks about [defenders as] nameless, faceless victims. That's what they are."

How many victims has Mark taken this season?

"A lot," he said. "Us as a team, we've taken a lot. And we plan on taking a lot more."