Over the last three seasons, the Stanford Cardinal defense has made a habit out of proving people wrong, but 2015 might present the toughest test yet — by a long shot.

Since the departure of Andrew Luck in 2011, Stanford’s defense has emerged as one of the elite units in the country, a terrifying mix of power up front, speed on the back-end and a physical, downright mean brand of football across the board. In fact, the Cardinal defense has been so good in recent years that Stanford not only withstood the inevitable decline in offensive production after Luck’s graduation but actually improved, winning two consecutive Pac-12 titles and bringing a Rose Bowl trophy back to the Farm in 2013.

Along the way, there have been doubters. Plenty of doubters. But in each case, the Cardinal have succeeded in not just silencing the critics, but slamming their mouths shut with an even better performance the following year.

Losing locker room leader Chase Thomas to graduation? No problem. The Stanford defense returned to the field in 2013 better than ever, capped off by a near-flawless performance against Marcus Mariota and Oregon.

How about the next year? Saying goodbye to legends Shayne Skov, Trent Murphy and Ben Gardner in 2014 — not to mention defensive coordinator Derek Mason? Replicating anywhere close to the results of 2013 would be cause for celebration, right? Instead, Stanford put up better numbers most of the year.

However, this year might take something extra special out of defensive coordinator Lance Anderson — a veteran of the program since the early days of Jim Harbaugh — and the Cardinal coaching staff to keep the Stanford defense from dropping off a steep cliff.

Admittedly, I have a hard time believing that there will be a drop-off in Stanford’s defensive performance since this team seems to fill gaps and make adjustments better than just about anybody. The Cardinal’s offensive struggles this past season, though, suggest that this program isn’t completely impervious to the pains of rebuilding. As a result, this just might be the year that Stanford’s otherworldly defense finally comes back towards Earth.

In particular, Stanford will be hard-pressed to find answers in the secondary and on the defensive line. With mounting speculation that fifth-year senior cornerback Lyons will head to Michigan as a graduate transfer, Stanford’s back line will receive a complete makeover in 2015. Stellar safety Jordan Richards has exhausted his eligibility, and so has fifth-year senior free safety Kyle Olugbode. Junior Alex Carter, who has been a key contributor since his freshman year, has opted to enter the NFL Draft.

It’s a perfect storm of trouble for Stanford in the secondary, a Sharknado merged with a volcano. Losing every player with meaningful playing time from last season with the exceptions of Ronnie Harris, Terrence Alexander and Zach Hoffpauir means that Stanford will have to play some very young blood in 2015. And in a pass-happy, fast-paced Pac-12 conference that feasts on mistakes, this inexperience could become a major concern in 2015.

Nevertheless, Stanford does have a lot of promising talent to plug in — it’s just a question of whether they will be ready. Despite missing out on big-time safety recruits Kirk Tucker and Arrington Farrar in last two seasons, the Cardinal did succeed in bringing in 4-star corner Frank Buncom and hard-hitting safety Ben Edwards in the most recent recruiting class. If Lyons does depart, Buncom might be called into duty right away. But if he is not ready to play right away, where does that leave Stanford? Hoffpauir is probably locked in at safety, as is Harris at corner. Kodi Whitfield could very well take the vacant free safety spot, but that other cornerback slot vacated by Lyons (if he does leave) remains very up in the air.

A similar question looms on the defensive line, which loses all three starters from last season: David Parry, Henry Anderson and Blake Leuders. While Aziz Shittu seems the natural and obvious heir apparent to start wreaking havoc in the backfield, he is still recovering from a knee injury suffered midway through last season.

Sophomore Harrison Phillips was unexpectedly thrown into the action last season due to severe attrition along the line, but will he or his classmate, highly touted recruit Solomon Thomas, be able to take the next step and match the production of their predecessors?

The most intriguing players who could factor into the defensive line discussion next season are seniors Luke Kaumatule and Jordan Watkins, along with true freshman Wesley Annan. Kaumatule and Watkins haven’t broken through the depth chart in their Stanford careers, but they have been with the program for almost four years now and could make that move up the ranks this offseason.

Annan is enormous and comes in at a time when the Cardinal have a desperate need for a run-clogging force up the middle with Parry’s graduation and Ikenna Nwafor’s medical retirement. Like Buncom, it’s unclear right now if he will be able to play right away, but his development might be crucial to the success of the defensive line in 2015.

Ultimately, Stanford has the talent to reload defensively. It’s going to come down to developing that talent, and in that department the Cardinal happen to have the best in the business — Duane Akina and Randy Hart, especially. Say what you want about some of David Shaw’s in-game decisions, the man can flat out hire. High-quality assistants and developing talent quickly will probably be the key for the Stanford defense to overcome this latest — and possibly strongest — wave of doubters yet.

If I have learned anything at Stanford to this point, it’s that you don’t doubt this football team when it comes to responding to challenges. Last season may not have gone so well, but don’t forget the way Stanford closed things out. Can we expect the defense in 2015 to be just as dominant as its predecessors? Probably not, but it will certainly be fun to see what Stanford’s young guns can do — and to get an idea of how scary this unit can be in a couple of years.

Vihan Lakshman has been working all offseason to rid himself of any doubt he has about Stanford football’s 2015 prospects. Let him know what you think of the team at vihan ‘at’ stanford.edu.