If you’ve ever imagined the puppets of “Sesame Street” cursing, doing illicit substances, and many other R-rated activities, and wondered, “Why isn’t there some actual media production that makes my dream a reality?” then I am your hero today. Feast your eyes -- or ears -- on the hit Broadway musical, Avenue Q, which essentially is an adult version of the hit PBS children’s show. One of the premier songs in the show is “It Sucks To Be Me.” Each character introduced tops the others with their utter misery and ennui, with the phrase, “it sucks to be me.”

Even Puppet Gary Coleman would agree, though, that it sucks the most to be the San Francisco 49ers’ defense right now.

What happens in Levi’s Stadium this year also might not be appropriate for children’s eyes and ears, as the Niners defense has hemorrhaged talent this offseason. It hasn’t mattered what point in their careers, or by which means they’ve left; the San Francisco defense is lacking much of its top talent and leadership from the 2014 season. How will this affect their defense’s success in 2015 and their chances of winning?

Schadenfreude

Schadenfreude is a German word that essentially means “finding joy in the misfortune of others.” Yet another song in the score of Avenue Q, this is a feeling that most other NFC teams must be experiencing at the expense of the Niners. What happened to shake our confidence in the security of these former defensive juggernauts?

First and foremost, the entire linebacking corps was decimated. They lost two 2014 stalwarts to retirement, one an established star in the league and the other a blossoming rookie. The first, veteran inside linebacker Patrick Willis, retired on March 10th due to complications with a big toe injury. The 30-year-old Willis had suffered this injury multiple seasons ago and watched it sap away much of his effectiveness as a player. After putting together 174 total tackles and four sacks in his stellar rookie season, the annual Pro Bowler compiled full-season paces of just 120 and 91 tackles in his last two seasons.

Similarly, 2014 rookie Chris Borland came on in Week 6 in relief of Willis and amassed an insane 101 total tackles in those following eight starts. Borland had played through concussion concerns in college at Wisconsin and then was placed on season-ending Injured Reserve with an ankle injury in late December. He retired just a week after Willis, citing his long-term health as his motivation.

Retirement also claimed the heart and soul of the defensive line for these 49ers this past week: defensive lineman Justin Smith retired at age 35, after 14 seasons in the NFL. This underappreciated and versatile player garnered never reached double-digit sacks but always proved to be a disruptive force on the Niners’ and Bengals’ defensive lines.

Free agency also saw quietly productive veteran backup Dan Skuta depart to join the Jacksonville Jaguars. Starting cornerbacks Chris Culliver and Perrish Cox -- both top-40 options in 2014 by Pro Football Focus’s grading -- also left for greener pastures, with the former moving to Washington and the latter joining the Tennessee Titans.

With this much high-profile turnover, what can we expect the 49ers’ defense to look like in 2015?

There’s A Fine, Fine Line

Before we go predicting all sorts of doom and gloom for the boys from the Bay Area, let’s set ourselves some sort of production precedent. The best way to analyze the value of a defensive unit is to, obviously, look at the defense’s production as a whole. To do this, we’ll turn to our old friend here at numberFire, Net Expected Points (NEP). NEP helps us take the numbers we get from the box score and assign them contextual value so they relate even closer to the game on the field. By adding down-and-distance value, we can see just how much each play and each player influence the outcome of the game. For more info on NEP, check out our glossary.

We don’t have specific player Defensive NEP tracking as of yet, but we do have team Adjusted Defensive NEP, both measuring an entire defensive unit’s effectiveness against the run and the pass. The table below shows the 49ers’ marks in these categories -- and their league ranks as well -- since 2005, in order to give us some idea of how these players changed or sustained the defensive culture of this team. Remember: the lower or more negative an NEP value in Defensive NEP, the better.

As we can see from the above, it’s been a pretty up-and-down decade for San Francisco’s home team. In 2005, the Niners were one of the absolute worst teams in the league on the defensive side of the ball. They actually were somehow spiraling downward, as 2006 saw them bring in a worse Adjusted Defensive NEP and Adjusted Defensive Rushing NEP, despite improving their rank one spot in the former.

All of that changed, however, in 2007, which is marked with an asterisk for a reason. This was the first year that rookie linebacker -- drafted 11th overall out of Mississippi -- Patrick Willis played in the league, and he was a run-stopping revelation. While we obviously can’t chalk up an entire unit changing because of one player, his practical and intangible contributions were enough to make a very important impact on his pro team. In part due to Willis, the Niners went from the 28th-ranked team in Adjusted Defensive Rushing NEP in 2006 (giving up 22 points on the ground more than average) to the 12th-ranked squad in this metric (saving nearly 22 points more than average against the run).

In fact, we see a few very clear ticks upward in production for this defensive unit, possibly as a result of the additions to the squad -- though it appears sometimes this was delayed by needing time to gel. This may have been the case in 2008, as the addition of Justin Smith and defensive tackle Isaac Sopoaga had no immediate effect on the team. In 2009, however, no impact players were added in free agency or the draft to the defensive unit, but the team still took a major leap forward in its defensive prowess, setting the tone for itself in the early 2010’s.

Mix Tape

Where do we go from here, though? Already, from 2011 onward, we’ve seen this unit slip gradually in its production each year. This has corresponded nearly perfectly with Willis’ injury problems, as 2011 was the first year he played fewer than 15 games in a season, and every year since, he had fewer tackles and fewer games played. Without a crazy tackling machine like Borland to naturally fill Willis’ flow-and-chase role, much will be expected of the 29-year-old Michael Wilhoite as he slots in next to Navorro Bowman in the middle of the 49ers’ defense. What will likely happen is that Bowman will take much of Willis’ former production and duties as a roving defender, but Wilhoite will maintain the middle almost like a 4-3 MIKE linebacker.

As for the passing defense, the 49ers already slipped to 14th in the league last year in Adjusted Defensive Passing NEP, and that was with two highly-regarded defenders there. Shareece Wright and Tramaine Brock are fine players, but they’re not the proper plugs for the back end of this leaking defense.

First-round rookie defensive lineman Arik Armstead will likely take over Justin Smith’s left defensive end spot (5-technique), though this is perhaps the worst possible option for his development. The former Oregon Duck has size and physical upside to burn but has not yet refined his technique or pass rushing skills. By being thrust into a starting role, he may not get a chance to do so. For his sake, and the Niners’, I’m praying for a steady relief of Quinton Dial and Tank Carradine to spell him.

It’s going to be a rough rebuilding process for San Francisco, but this shouldn’t only be seen as the end of one era; it’s very clearly the beginning of a new one. Every ending is a chance to redefine the next beginning. In the short term, I will be very surprised if the Niners are in the top-half of our league rankings for Adjusted Defensive NEP at the end of 2015. Already on a downward trajectory before this, I would expect them to finish between 20th and 23rd in the league.

In the long term? Who knows, but perhaps they’ll be laughing at our pratfalls instead of the other way around.