The Wildcats' senior signal-caller is being touted by the school as a Heisman candidate, complete with slick marketing campaign. He led the Big Ten in completion percentage and his team in rushing last season, despite playing just 10 games due to a ruptured Achilles tendon in Week 10.
If he completed his comeback from injury in time for Saturday's game, just 10 months into a recovery that normally takes 12-14 months, and led the Wildcats onto the field at Alumni Stadium, it would have made for quite a story -- and a challenge for the Eagles.
Persa didn't finish off that storyline Saturday, as he didn't dress for the game. Kain Colter, his sophomore understudy, took his place in pads under center.
If the Eagles' defense, especially the beleaguered secondary -- which lost both presumed starting safeties (Okechukwu Okoroha -- dismissal; Dominick LeGrande -- transfer) in the span of a week toward the end of camp and was without starting corner Donnie Fletcher (back injury) -- took a sigh of relief at the sight, it shouldn't have.
Colter made some decent plays with his arm (throwing for 197 yards) but it was the plays he made with his legs (rushing 23 times for 71 yards and a touchdown) that killed the Eagles. The shifty QB was part of a Northwestern rushing attack that piled up 227 yards, the first time a team accumulated more than 200 in a game against the Eagles since Virginia Tech in 2009, and scored three touchdowns.
In 2010, the Eagles had the country's best defense against the run. It allowed an average of 82 yards a game.
"He moved real well," Luke Kuechly said of Colter. "We were preparing for Persa, he moves really well, but this guy moves just as well.
"He presented a lot of difficulties, especially when he was getting outside the pocket," Kuechly added. "He had some big runs that kind of cut us up."
With BC ahead 10-3 in the second quarter after Kuechly intercepted a Colter pass and returned it to the NU 2-yard line to set up an Andre Williams score, the Wildcats got the ball back at their 20. Colter calmly moved the ball downfield, finding open receivers and gaining yards himself when necessary. With the ball at the BC 9 after a false start, Colter ran right and had a shot at the end zone before Kuechly pulled him down.
On the next play, Colter went right again and again Kuechly met him at the edge, but this time the Wildcats QB slipped through the Eagles 'backer and into the end zone to even the score.
"We were softer than we need to be, than we're accustomed to being," BC head coach Frank Spaziani said of the defensive line, another culprit in the unusually porous pass defense. "We had some mental mistakes out there that hurt us, too."
It couldn't have helped that senior defensive tackle Kaleb Ramsey, who Spaziani has said he believes could be in for a big-time season, left the game in the first quarter with a left foot injury and didn't return. The fast pace that the Wildcats used probably didn't help, either.
"I think some of the down linemen, their metabolic pace looked like it ..." Spaziani pantomimed a line rising, then falling, "... dropped off a little bit there. We had to substitute some guys. That happens with inexperienced guys, but I think it might've been magnified [by the pace]."
"I think it's difficult when you face a team that had a tempo like that because you can't replicate it in practice," Kuechly said.
"I thought we controlled the line of scrimmage pretty well," Northwestern coach Pat Fitzgerald said in his postgame remarks to the media. "We understood and respected their front seven, but we knew the tempo would play to our advantage, especially on a warmer day."
The temperature at game time was 73 degrees.
What did the Eagles need to do better Saturday afternoon?
"Pretty much just hustle to the ball," linebacker Kevin Pierre-Louis said. "We knew the plays they were running, we just need to get to the ball faster."
And so while the much-talked-about offense at times produced big chunks of yardage -- Williams broke a 69-yard run on the first play from scrimmage, Chase Rettig piled up 375 yards passing and Ifeanyi Momah pulled down eight passes for 157 yards -- and at least had a chance to tie it in the fourth quarter, it was the presumed strength of the Eagles, the run defense, that let them down.
"Congratulations to Northwestern. They came in here and did what they had to do," Spaziani said. "... They had entirely too many yards on the ground. We made too many mistakes. We played too sloppy to win a game like that."
Jack McCluskey is an editor for ESPN.com and a frequent contributor to ESPNBoston.com.