Known commodities: The Wildcats welcome back 16 starters, including All-Big Ten quarterback Dan Persa, leading receiver Jeremy Ebert and leading tackler Brian Peters.

Questions: Who will replace Keegan Grant at guard and No. 2 wide receiver Sidney Stewart? Productive linebackers Nate Williams and Quentin Davie are gone, as is standout defensive tackle Corbin Bryant. Need to improve what was conference’s worst run defense during Big Ten play last year. The ‘Cats allowed a Big Ten-high 28 sacks, and on the other side of the ball their eight sacks were one more than Minnesota’s conference-worst seven.

Spring game recap: With starter Persa on the sidelines as he recovered from an Achilles injury that ended his 2010 season prematurely, three Wildcat quarterbacks combined to complete 17 of 35 passes for 151 yards in a controlled scrimmage. Evan Watkins was the most efficient as he completed 7 of 11 attempts for a game-high 70 yards and a touchdown. Trevor Siemian tossed for a pair of touchdowns but was only 5 for 14 for 46 yards while Kain Colter was 5 for 10 for 35 yards. Kain also led the team with 42 yards rushing on four scrambles.

Issues addressed: Persa is expected to be 100 percent or close to it before the start of preseason practice, and that seems to be a good thing after none of his backups created any separation during spring practice.

“I think if I were to look at all three, all of them have improved,” head coach Pat Fitzgerald said. “Over the last week, Evan has improved his footwork and balance. He was really throwing the ball well this last week. I think Kain’s arm strength is getting better, in comparison to what it was when he reported. When he reported, he was coming off that labrum injury and it was tough. He is getting stronger. Trevor is a guy that was unknown because he wasn’t in the mix in the fall, and he has gotten better each week. So I think all three have improved, not necessarily one more than the other. That’s the goal of spring, to watch all these guys get better.”

Quarterback was a big topic of discussion during the spring in part because the Wildcats enjoy the return of 16 starters, including nine on offense, but Fitzgerald was on the lookout for two new linebacker starters as well as a replacement for standout defensive tackle Corbin Bryant and cornerback Justan Vaughn.

Senior Ben Johnson and junior David Nwabusi were listed as new starters coming out of spring while senior Jeravin Matthews grabbed the open cornerback spot and junior Brian Arnfeldt and senior Niko Mafuli were listed as co-starters at tackle.

“We wanted to get our attitude back,” said Fitzgerald, whose team closed the season with three consecutive losses after Persa was injured in an upset of Iowa. “I believe we’ve done that. The guys are having fun, they’re competing their butts off, it’s been a real physical spring. And we’ve solidified some competitive depth. Coming out of spring, this will be the most depth that we’ve had. So that encouraging.”

Advanced statistical revelations*: The Football Outsiders numbers might be lukewarm on Nebraska, but they pretty much can’t stand Northwestern (which is kind of ironic if you think about the school’s well-earned academic reputation). An adjusted score measurement dropped the ‘Cats to a staggering 2-11 from their real mark of 7-6 last season, although it interestingly found they should have beaten Iowa worse based on how they played.

Offensively, Northwestern played fast and offered good play-call variability, but a complete lack of playmaking ability hampered the attack. That was despite good consistency, especially on the ground.

The defense was terrible on early downs but decent on third with stopping the run a particular bugaboo, and that nearly nonexistent pass rush probably hindered what had the makings of a pretty good secondary (I have always liked Jordan Mabin’s gumption at cornerback, and David Arnold joins Peters as a big, solid safety).

Pro prospects**: Persa has so-so arm strength but excellent accuracy, and the evaluator appreciates not only his running skills but also calls him a winner.

Offensive tackle Al Netter looks more like a guard in the NFL because of his power in the run game. Lacks range to want to see him exposed too much on the edge but has good quickness to help compensate.

Defensive end Vince Browne: Admirable frame but not much else in terms of what NFL teams are looking for. Hard worker who needs to work on playing lower to be able to use power better

Mabin: Looks good in zone and press bail coverages. Possesses decent speed, will run with receivers and plays the ball well in the air. Size limits him against the run, but he is a willing hitter.

Issues remaining/other thoughts: The season hinges on the health of Persa, who must be monitored because even with the advances of sports medicine in the past two decades, full recovery is never truly a sure thing.

Return of solid running back Mike Trumpy and addition of some interesting youngsters offers running game a chance to improve, especially if Persa picks up where he left off as a scrambler.

Persa can count on a lot of experience at wide receiver although explosiveness might still be lacking.

The offensive line’s chances to improve are enhanced by the return of almost all of the two-deep.

Almost all of the two-deep is back in the secondary, too, but linebackers are somewhat unknown.