Arik Armstead has been a stud this season. Let’s get that out the way. The former Oregon Duck’s rise over the course of this otherwise largely painful campaign has been mostly ignored, but it has certainly created an interesting dilemma for the front office this offseason and beyond. Armstead hasn’t just been blowing it up as a big end, his primary position. He has also been moved inside more to nose tackle in nickel - a development that, paired with Solomon Thomas playing more 3-tech, has the potential to produce a significant re-jig of the 49ers’ defensive line rotation heading into an offseason when the team surely adds the upper tier edge rusher they’ve been craving since Aldon Smith departed.

Even as a rookie, Armstead’s potential as a destructive force was clear, despite his rawness. He looked like a player who could be dominant against the run and pass for a long time. Unfortunately, two injury-plagued years followed — years when Armstead was supposed to develop into that destructive force. Not only was he injured, but he had to learn two new schemes, and in the 2017 season, had to shed weight to play LEO — hardly his most obvious position. His absence for much of those two seasons left the 49ers front office in a difficult position, facing a decision to pick up the players’ fifth year option based largely on potential. The Jacksonville Jaguars had a similar decision with their 2015 first rounder, Dante Fowler Jr. They decided not to pick up the option, and Fowler was later traded to the Rams.

The 49ers however, had seen more from Armstead. Someone who is regularly reported to be blowing up practice and who always showed a tantalizing amount of freakish ability even amongst the forces of nature gracing NFL fields, Armstead was preliminarily signed on to play out his fifth year on his rookie deal.

Then this season happened, and judging yb Armstead’s continued improvement, we haven't seen the last of his impact. A key part of evaluation is knowing what direction a player is trending. Armstead is trending right up. For the season as a whole, he has a 79.9 grade from PFF. Since Week 4 he has an 87.1 grade. Since week 10 he has an 88.3 grade. The film backs this up — Armstead is going from strength, to strength, to strength.

Most significantly, he has been an elite run defender, increasingly at two spots. The significance of his positional versatility will become clear shortly. But the statistics and the film reveal a monster of a run defender, who can manhandle whoever an offense throws at him. At 6’7 and over 290 lbs, this was always a distinct possibility with Armstead.

Armstead is aligned opposite #74 on the right side.

According to PFF, Armstead is the first to contact the ball carrier on 13.49% of his run defense snaps, second in the league behind Calais Campbell, one of the most highly regarded and destructive linemen in the entire NFL. Armstead has an overall run defense grade of 87.4, good for third in the league behind Campbell and Jadeveon Clowney. His run defense has been better than Khalil Mack’s and JJ Watt’s. Armstead is amongst the elite.

Every game, he absolutely obliterates whoever is trying to block him on at least a couple of occasions. Tight ends? Don’t even bother trying to block Armstead with tight ends. Lone offensive linemen struggle with Armstead. It’s why you see him double teamed, and why we’ve seen his usage at nose tackle in nickel packages grow in recent weeks.

Armstead is aligned on the left side opposite 82

Armstead is number 91 on the right side of the formation

Armstead is aligned at 1-tech between 60 and 68

Whilst his run defense has been good, his pass rush is something many fans will point to as being inadequate, primarily because he has only three sacks on the season. This statement is then normally followed by a suggestion that the 49ers can replace Armstead with a combination of Jullian Taylor, Solomon Thomas and Kentavius Street, and that his lack of pass rushing impact doesn't justify the contract he would likely demand.

There are many responses to that. The first of which, is that sacks aren’t always reflective of pass rushing impact. DeForest Buckner was a great example of that last season. In fact, for the whole of last season Buckner had 52 pressures of which four were sacks. This season, he’s had 48 pressures so far, of which 10 are sacks. See the problem with sack numbers? Armstead is having a year much like Buckner did last season - having a rather notable impact as a pass rusher without having the sack numbers to pad his resumé.

Armstead actually leads the team in pass rush productivity per PFF, but he has had fewer opportunities than Buckner. The cause of this is largely because the 49ers lack a legitimate edge rushing threat, so have really only had room for one true interior rusher as they need flexibility with who is rushing. This season, the 49ers have required defensive ends and linebackers on the field who can rush and cover — much of their pressure has come from some level of deception. Despite his lack of sacks, Armstead has taken his opportunities when rushing the passer, though perhaps none were as impactful as this rep vs Indianapolis.

Armstead lined up at LDT.

The second response to the claim that Armstead is replaceable, is to draw attention to his versatility. As well as playing big end, and being capable of lining up at 3-tech, he has been utilized at nose tackle in nickel packages a considerable amount recently. Last week against Denver, Armstead played almost a third of his snaps at nose tackle. The week before he played over a quarter of his snaps at nose tackle. In theory, nose tackle is a position requiring a shorter, stouter player capable of taking on double teams — but Armstead has proved quite capable at the position, and offers a far superior threat as a rusher from that spot than either Earl Mitchell or DJ Jones.

That versatility is, at least in the immediate short term (of real significance to this staff by now), unlikely to be replicated by anyone else, or really be effectively replaced by a rotation of players. In a passing league, a nickel nose tackle who can hold up against the run but also rush the passer is one of the rarest types of player to find. Armstead is not Tank Carradine, a player who just played at big end to a high level vs the run. He does considerably more than that.

So what does this mean for the 49ers? Perhaps most importantly, it should have created the impetus to keep Armstead in the Bay for at least the duration of his fifth year option and quite possibly beyond. This staff is going into its third year at the helm, and the reality is they can't afford to let their best players walk away in the hope that the younger players behind them fill the significant void they would leave. They need to see a marked improvement in results next season — second in the division is perhaps the minimum achievement that will be acceptable along with a record above .500. Whilst the likes of Malcolm Smith, Pierre Garćon, and even Earl Mitchell have failed to separate themselves from those behind them on the depth chart, Armstead decidedly has. That kind of talent cannot be let go.

Furthermore, Armstead’s ability and versatility can change the composition of the 49ers defensive line room. Purely on ability, his destructiveness vs the run forces defenses to double team him. This tends to opens up favorable 1 on 1s for other players (especially with Bucker also being doubled), notably the nose tackle and the SAM linebacker in base packages. DJ Jones excels when blocked 1-on-1 (he struggles more against double teams at less than 300 lbs), where his lateral mobility and stoutness creates real issues for opposition offenses. Armstead has allowed the 49ers to use Jones over Earl Mitchell - who is better against double teams. Ensuring the SAM is kept cleaner has allowed the 49ers to go towards more of a coverage linebacker in the role, crucial in a passing league.

Additionally, if defenses have to give Buckner a 1-on-1 in nickel packages with Armstead at nose tackle, that’s a massive win. If defenses double Buckner, Armstead will blow things up. Not only is it freeing up the 49ers, it’s a catch 22 for offenses as well.

To address the versatility point, Armstead (and Solomon Thomas’ improvement) may also allow the 49ers to move on from a couple of players. The move from Earl Mitchell to DJ Jones (at least in part enabled by Armstead), plus Armstead being capable of playing at nose tackle, sees Mitchell fall to essentially third on the nose tackle depth chart. This is no knock on his performances (he’s been good) - but the reality is teams are unlikely to want to carry a third nose tackle option, so Mitchell could be on the move.

On top of that, Sheldon Day, who was often the game day 3-tech and 1-tech backup, has seen those roles taken by Armstead and Thomas. That’s another player who, despite playing well, could be on the move. Waiver claims have less value to teams than their own draft picks and proven studs (even if they are holdovers). As a result, the 49ers could bring Kentavius Street and Nick Bosa (*touches wood*) onto the roster without making any other moves. In a passing league, that seems like an upgrade. The 49ers will be comfortably two deep at each position on the defensive line and will be primed to enter the best defensive line in the league discussion. Armstead’s development will have contributed significantly to that.