But the 5-foot-8, 180-pound junior has been just as productive as his powerfully-built peers. Mark has also given Northwestern a home-run threat at tailback that his team has lacked in recent years.
"He can run the ball in the zone play, run the ball in the option," said Michigan State head coach Mark Dantonio. "He's elusive. He's got a next gear. His size, he's smaller in size, but he packs a punch. He runs powerfully, can break tackles. I think he's a very good running back."
Mark has been surprisingly durable.
"I would say that it is his heart," said sophomore safety Kurtis Drummond. "He is a tough kid, he's elusive, and maybe he isn't taking as many big hits as he could. He is hanging in there, so that is a big credit to him and the kind of heart he's got."
Mark ranks No. 14 in college football in rushing yards per game (118.10) and third among Big Ten tailbacks behind Bell (124.90) and Ball (122.60). The junior from Texas enters this weekend's game at Michigan State with 1,176 rushing yards in 10 games. Mark has rushed for 100-yards plus in four straight games and seven total in his first year as starting tailback for Northwestern.
"Part of their brand of football is being tough, scrappy and things of that nature," said senior linebacker Chris Norman. "He represents their program well."
Michigan State has faced 10 tailbacks ranked among the Top 100 in college football in rushing yards per this game season. And most of the those running backs have been held well below their per-game average by the Spartan defense.
Mark, however, presents a different type of challenge than the tailbacks that Michigan State has faced in 2012.
"We have faced a lot of great running backs, but we haven't faced anybody like that yet," said junior defensive end William Gholston. "He is really fast. He seems to squirm through holes. You watch film and it looks like the play has stopped and he squirms through the hole and he will get a big gain, like 80-yards plus."
"He is a great player," added senior nose tackle Rashad White. "Just watching him on film, he is quick and if you don't wrap him up he is going to be able to break loose and get as many yards as he can... you can't give him space because he'll wiggle through and break right on through. We've got to wrap him up and not give him the opportunity get into space."
Notre Dame senior Theo Riddick is the only other tailback Michigan State has faced this season that presents the home-run threat out of the backfield that Mark gives Northwestern.
"He is definitely an explosive player, a home-run hitter any time," said Drummond. "Basically, you've got to just bottle him up and get hits on him. It will definitely be a challenge, but we are looking forward to the challenge."
Michigan State possesses the speed on defense to bottle up Mark. But limiting the big-play ability of the Northwestern tailback will be an 11-man effort.
"He's got a great burst and he can take it to the house if you don't have 11 hats to the ball," said Norman, "and you don't execute your assignment and do your job on defense."
Mark's impact on the game extends beyond offense. The Northwestern junior is a game-changer on special teams.
"He is a guy that you see making plays every week," said Spartan linebacker Max Bullough, "whether he is returning kicks, whatever he is doing. He is making plays, scoring points for them. We need to understand where he is on the field and cover him."
Mark tied his career-high with 281 all-purpose yards in victory over Syracuse in Week 1. He would have gone well over 300 all-purpose yards last weekend at Michigan if Big Ten officials hadn't thrown a penalty flag on a kick that Mark returned for touchdown.
"Great punt returner, great kick returner, two touchdowns on punt returns this year," Dantonio said. "Kick return called back against Michigan on an officiating call that I'm sure they'll be concerned about as well, very concerned about."