You can probably spread around the fault for the San Francisco 49ers' capitulation to the Houston Texans on Sunday amongst several units.
Receivers dropped passes, corners failed to cover, which was especially egregious considering the Texans had (at best) two NFL-calibre receivers playing in the game, and no one on the Niners offense besides Mac Jones really sparkled.
However, the most concerning part of the performance was one that had already shown up on multiple occasions throughout this season.
And judging by this performance, they're not getting any better in a hurry.
Most football games are won in the trenches. That's just a fact, and until they change the rules of the game, it will always be a fact. Teams cannot win without strong (or at least effective) offensive and defensive lines.
The 49ers have been proof of this in years past, with lines built on Bill Walsh and Bobb McKittrick's zone blocking, or the more power-based days under Jim Harbaugh. Linemen like Randy Cross, Harris Barton and, in more recent days, Trent Williams, have been standard bearers for O-lines that could push the pile and also protect their many legendary quarterbacks.
Meanwhile, on the defensive line, players like Dwaine Board, Charles Haley, Justin Smith and Nick Bosa have been standard-bearers for defenses that have terrified offenses and knocked quarterbacks off their game.
As it stands currently, the 49ers, besides an ageing Williams, have none of these players.
Now, injuries to Bosa, Bryce Huff, and even Ben Bartch have knocked San Francisco's trenches off-kilter, that can't be denied. But it still doesn't excuse the execrable performance put forth by both interior lines in Sunday's loss.
It turns out you can make one of the best running backs in NFL history look pretty average if you have Connor Colby, Matt Hennesy and Dominick Puni, whose regression has been alarming, blocking for them. There were barely any open holes in the run game, and their pass protection might have been even worse. This has been a recurring theme for the 49ers' three interior linemen throughout the season.
While some would focus on right tackle Colton McKivitiz's struggles, he was at least facing a top-class pass-rusher in Will Anderson. The Niners' interior O-line could neither move nor protect against the otherwise middling Texans defensive line, with them frequently blowing up run plays and pushing pressure into Jones' breadbasket.
Of the defensive tackles available, only Jordan Elliott is missing with injury (aside from the baffling decision to deactivate CJ West), and he left the game late. Hence, depth isn't an excuse here. Despite that, San Francisco summarily failed to stop the run on multiple occasions, making what was already an easier game for Texans quarterback CJ Stroud into a cakewalk.
The Texans were able to run the ball at a solid clip throughout the game, allowing themselves to consistently be in advantageous second- and third-down situations, and given the defense's inability to cover even the most basic of pass routes on Sunday, that was a death knell to the 49ers' chances of success.
Where you can make an excuse is in the pass rush. By the end of the game, the 49ers barely had enough defensive ends to play their base defensive setup, so expecting pass-rush production out of most of these players, some of whom are barely practice squad fodder, is asinine.
You can account for these deficiencies. You can help your offensive tackles by putting together a quick-release passing game and combining it with a solid run game, just as the Niners did the previous week against the Atlanta Falcons, or earlier this season against the Los Angeles Rams. On defense, you can cover up holes in your pass rush by generating some noise inside and unsettling the quarterback.
That's been a trend around the league in recent years, thanks to the likes of former Rams All-Pro defensive tackle Aaron Donald, and it's led to the knock-on effect of guards and centers, previously the poor relations of the O-line group, being paid the big contracts normally reserved for the tackle position.
Sadly, the 49ers have no impact players in any of the interior positions that allow them to do this.
Some would have the Niners target a pass-rushing edge at the trade deadline, with Trey Hendrickson and Maxx Crosby among those mentioned. However, this observer sees a bigger issue at the defensive tackle spot, where a disruptor who can provide some interior pass rush while fortifying the team's run defense -- someone like the Tennessee Titans' Jeffrey Simmons, perhaps -- could have a bigger overall impact on the defensive unit.
That, coupled with the return of Bartch to the offensive line, might just stop the 49ers' season from taking in water.
It's too late for Sunday's game, though.