Kyle Shanahan doesn't care about your fantasy team. Honestly, he probably doesn't even care who started the game last week if he thinks a different guy has a better "feel" for the outside zone on a rainy Sunday in November. Trying to nail down the SF RB depth chart is basically like trying to catch a greased pig in a dark room. You think you’ve got a handle on it, and then suddenly, some rookie you’ve never heard of is taking goal-line carries while your $15 million superstar is pass-protecting for three straight series. It’s frustrating. It’s chaotic. But it’s also the most productive rushing system in the NFL, which is why we’re all so obsessed with it.
The 49ers' backfield isn't just a list of names on a piece of paper. It’s a living, breathing hierarchy that shifts based on calf strains, defensive fronts, and how much Shanahan trusts a guy to pick up a blitz.
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The Christian McCaffrey Factor and the Reality of Workload
Let’s be real for a second. When Christian McCaffrey is healthy, there isn’t really a "depth chart" in the traditional sense. There is CMC, and then there is everyone else waiting for him to breathe hard so they can get a single snap. He is the sun that the entire San Francisco offense orbits around. But as we saw throughout the 2024 season and heading into 2025, that workload comes with a massive tax. Achilles tendinitis isn’t something you just "shake off." It lingers. It flares up. It makes a 28-year-old RB look like he’s walking on eggshells during training camp.
Because of those injury scares, the SF RB depth chart has become more of a committee-in-waiting than a true bell-cow situation. You can't just look at the RB1 spot and ignore the rest. Shanahan has learned—sometimes the hard way—that he needs a "CMC-Lite" and a "Hammer" to survive a 17-game gauntlet.
When McCaffrey is off the field, the geometry of the offense changes. You lose that elite receiving threat out of the backfield that forces linebackers into impossible decisions. That’s why the backup spots are so heavily contested. They aren't just looking for a guy who can run; they’re looking for a guy who can read the leverage of a defensive end in a split second.
Jordan Mason and the Rise of the Undrafted
Jordan Mason is the perfect example of why you can’t trust "draft pedigree" in Santa Clara. He was an undrafted free agent. He spent years grinding on special teams. Then, suddenly, he’s leading the league in rushing yards through the first month of the season because CMC’s legs decided to quit. Mason runs like he’s trying to break the earth's crust. It’s violent. He doesn't have the lateral twitch that McCaffrey has, but he excels in the "one cut and go" philosophy that the Niners' zone-blocking scheme demands.
However, Mason has limits. His hands aren't elite. If the Niners are down by ten in the fourth quarter, is he the guy they want out there? Probably not. That's where the nuance of the SF RB depth chart kicks in. You have different players for different scripts.
- The Early Down Grinder: Mason holds this down when the starter is out.
- The Third Down Specialist: This used to be the "Jeff Wilson Jr." or "Jerick McKinnon" type role, and the Niners are constantly auditioning new faces for this.
- The Gadget: We can't talk about the backfield without mentioning Deebo Samuel, who is basically an RB3 whenever Shanahan gets bored with traditional formations.
Isaac Guerendo and the Speed Metric
Then there’s the youth. Isaac Guerendo was the "shiny new toy" that had everyone buzzing because of his 4.33 speed. In this offense, speed is a force multiplier. If a defender takes a bad angle against a typical back, it’s a 12-yard gain. If they take a bad angle against Guerendo, it’s a 75-yard touchdown. We saw flashes of this in 2024—specifically that massive late-game run against the Seahawks that essentially iced the win.
But Guerendo is a rookie (or a young vet, depending on when you’re reading this) who struggled with hamstring issues early on. In Shanahan's world, if you aren't practicing, you aren't playing. The SF RB depth chart is built on trust. If you miss a pass protection assignment and Brock Purdy gets sacked, you might as well start looking at real estate in another city. Guerendo has the highest ceiling of the backups, but his floor is "inactive on game day" if he can't stay healthy.
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It's a weird dynamic. You have Mason, who is reliable and tough, versus Guerendo, who is explosive but unrefined. Most teams would just pick one. The 49ers just play whichever one had the better week of practice.
Why the "Shanahan System" Makes Everyone Look Good
People always say, "Anyone can run in that system." It's a cliché for a reason. Raheem Mostert, Matt Breida, Elijah Mitchell—the list of guys who came out of nowhere to put up 100-yard games is endless. The system relies on the "Outside Zone." The offensive line moves laterally, the defense flows with them, and the running back is looking for one specific crease. Once they see it, they plant their foot and explode vertically.
This is why the SF RB depth chart is so volatile. You don't need a generational talent to get 4.5 yards per carry in this offense. You just need a guy who is disciplined enough to wait for the block to develop.
- The Lead Block: Kyle Juszczyk is the secret sauce. He’s the best fullback in the league, and his ability to delete a linebacker from the play makes the RB's job 50% easier.
- The Threat of the Pass: Because Brandon Aiyuk and George Kittle demand so much attention, defenses can't just stack eight men in the box every play.
- The Motion: The Niners use more pre-snap motion than almost anyone. It confuses the "gap integrity" of the defense, creating lanes that shouldn't exist.
The Injury Bogeyman
We have to talk about Elijah Mitchell for a second, even if it's just as a cautionary tale. The guy was a stud. He broke records as a rookie. But his body just couldn't handle the violence of the NFL. He’s been a perennial resident of the Injured Reserve list. This is the dark side of the 49ers' rushing attack. They ask their backs to run hard, finish blocks, and play physical. It wears guys down.
When you're looking at the SF RB depth chart for your own scouting or just to understand the game, you have to assume that the RB2 is going to start at least four games. It’s almost a statistical certainty at this point.
Actionable Insights for Following the 49ers Backfield
If you're trying to stay ahead of the curve, don't just look at the box scores. You have to look at the "hidden" stats that Kyle Shanahan values.
- Check the "Green Dog" blitz pickups. If an RB misses a block in pass pro, he’s getting benched. Period. Watch the film or read the local beat writers like Matt Maiocco or David Lombardi; they usually point out who is struggling in pass protection during camp.
- Monitor the Wednesday Practice Report. This is the most important document of the week. In San Francisco, a "Limited" tag on Wednesday usually means nothing, but a "Did Not Practice" (DNP) on Thursday for a veteran like McCaffrey is a massive red flag that the backup is about to get 20 carries.
- Follow the "Fresh Legs" philosophy. Shanahan isn't afraid to ride the hot hand. If a backup gets a couple of big chunks early in a game, he will stay in. This isn't a team that cares about "equal touches" or "keeping guys happy." They care about winning the physical battle at the line of scrimmage.
- Draft/Roster Strategy: In any fantasy or betting context, you should view the 49ers' backfield as a single unit rather than individual players. If you own the starter, you must own the immediate backup. The drop-off in production is often minimal because the system is so dominant, but the change in personnel can happen in the blink of an eye.
The SF RB depth chart will always be a headache. It's designed to be flexible for the coaches and a nightmare for opposing defensive coordinators. Just remember: in Santa Clara, talent gets you in the door, but availability and pass protection keep you on the field. Keep your eyes on the practice reports and don't get too attached to any one name behind McCaffrey—because by next Sunday, it’ll probably be someone else's turn to be the hero.