Charles Rex Arbogast, File, Associated Press
In this Oct. 6, 2012, file photo, Notre Dame head coach Brian Kelly, center left, talks to his team during the second half of an NCAA college football game against Miami at Soldier Field in Chicago.

SOUTH BEND, Ind. — The biggest question has turned into the biggest surprise. And not the icky kind.

Notre Dame’s unexpected presence in the top five of the first BCS standings of the 2012 season, at No. 5, is undoubtedly driven by its defensive front seven and supplemented by a quarterback time-share arrangement that’s so quirky and unpredictable that it works.

But it could have all been undone by a rebuilding secondary that continues to confound all logic and ND fans’ worst fears.

At the halfway point of the season, the Irish are ranked No. 5 in pass-efficiency defense, the true measure of how easy or difficult it is to move the ball through the air on a given team. Last year ND, with standout safety Harrison Smith and three other multiple-year starters, ranked 58th in that category.

The front seven deserves some of the credit. The Irish have amassed 15 sacks and 26 quarterback hurries, the latter number on school-record pace (though the stat wasn’t charted in earnest until 2004).

But safety Zeke Motta and three converted offensive players have done their part too. Junior cornerback Bennett Jackson, in fact, finds himself fourth in the nation in interceptions this week (four in six games).

There are still plenty of other questions, though, about Notre Dame (6-0) as it rolls into the second half of the season Saturday against BYU (4-3). Here’s a look at the most intriguing of them and a shot at the answers:

Will Irish coach Brian Kelly change Notre Dame’s quarterback dynamic this week in light of another strong relief appearance by junior Tommy Rees?

Not if sophomore Everett Golson is healthy.

Kelly revealed Sunday that Golson did suffer a concussion on helmet-to-helmet contact Saturday with 3:24 left in regulation in Notre Dame’s 20-13 overtime win over Stanford, but that his No. 1 option is expected back in practice early in the week.

“He's going through the steps, the protocol that we have,” Kelly said. “He was still a bit symptomatic today, so he'll go through his cognitive testing (Monday), and we expect that if all things move in this direction that he should be cleared by Tuesday.”

Golson also has been playing through a turf toe injury he sustained in the second quarter of the Miami game on Oct. 6.

Kelly’s faith in Golson is based upon the sometimes obscured baby steps the sophomore is taking and the high ceiling he projects for him once he grows into the offense.

BYU presents another team that will test just how far along the growth curve Golson is. The Cougars and USC are the only teams left on the Irish schedule that, like Stanford last week, stuff the run, bring pressure against the pass and dare your quarterback to take shots down the field to make them pay for their gambling up front.

Oregon State, with the nation’s eighth-best passing offense, is the perfect antidote for what BYU likes to do defensively, and the Beavers thumped the Cougars in Provo, Utah, 42-24. Notre Dame, when it struggles to pass effectively, creates a feeding frenzy for what BYU likes to do defensively.

You have to run the ball into an overloaded box, which tends to put you in third-and-medium or long, which brings on even more pressure. “That's still our Achilles heel,” Kelly said. “We have to throw the football better.”

And sometimes that means getting Rees involved late, though Saturday’s relief appearance was evoked by injury, not Kelly’s trepidation that Golson couldn’t finish.

The dynamic of Rees relieving accentuates his strengths and minimizes his limitations. Teams can’t dedicate their game plan to a QB they may or may not see and whose skill set and mental edge is markedly different than the starter’s.

How does that look numerically? Rees has completed 68 percent of his passes (17 of 25) with one touchdown and zero turnovers. Last year, he had 19 of them.

How does ND’s passing attack stack up with the other national title contenders? Interestingly, while video game passing numbers get some national media goo-goo eyed, it doesn’t equate to sustained success. ND’s ranking of No. 86 in pass offense is better than every other team in the top seven of the AP poll except for Oregon, which is a still-modest 56th.

Where ND lags is pass-efficiency, though the Irish nudged up to No. 75 this week. All the other teams in the top seven of the AP rankings are in the top 35 in that category, save Florida (48th) and LSU (67th). Who will emerge as Notre Dame’s No. 1 running back?

It seemed like it was only a matter of time until last year’s 1,100-yard rusher, senior Cierre Wood, barked his way out of the doghouse after starting the season with a two-game suspension. And Wood, now just 29 yards out of the team’s rushing lead, likely will end up leading the team in rushing yards. But the three-man rotation of Wood, fellow senior Theo Riddick and sophomore George Atkinson, is an accidental dynamic that has come to serve Kelly well. Riddick is averaging a modest 3.8 yards a carry, but he gets tough yards against tough looks, and he’s Notre Dame’s leading receiver with 20 catches. By comparison, Wood and Atkinson have combined for three receptions.

Wood, though, is averaging 5.9 yards a carry and is ND’s most versatile back when it comes to running inside or out. Atkinson, at 9.1 per carry and with two runs over 50 yards, is the most explosive. “It's not only running the ball, it's the ability to catch the ball coming out of the backfield as well,” Kelly said, “and that's been the change this year from last year in terms of the complete running back. “Again, I think all three of those guys are continuing to work on being the complete back.”

Which is the toughest team remaining on the Irish schedule? Oklahoma is easily the most complete. The Sooners are No. 15 in total offense, No. 14 in total defense and in the top 15 in both kickoff returns and punt returns.

But it’s not necessarily the worst match-up. Teams with strong rush defenses give the Irish the most problems, and ND already has faced two (Michigan State rated eighth nationally, Stanford seventh) that are much better than Oklahoma’s (40th).

The Sooners do not effectively pressure the quarterback (76th in sacks), and they can get sloppy with the ball, but they’re easily the best offensive team the Irish have faced. To date, Miami, at 42 in total offense, is the best.

Are ND’s poll rankings this week the highest since the Holtz Era? No, it actually goes back only to the Weis Era. The last time the Irish were in the top five in both major polls was Sept. 10, 2006. The Irish were No. 2 in AP, No. 3 in the coaches poll two weeks into the 2006 season, before falling out of the top five and eventually finishing that season 17th.

Incidentally, ND’s highest ranking ever in the BCS standings is third. That happened during consecutive weeks in October of 2002. Does ND-Stanford’s overnight TV rating of 3.9, edging out South Carolina-LSU as the most-watched college football game of the day, mean the Irish are relevant again? That horse died weeks ago.