The 49ers' running-back depth chart doesn't make much sense once you get past Christian McCaffrey.

Their No. 2 running back is Elijah Mitchell, who's averaging 2.9 yards per carry this season. Their No. 3 running back is Jordan Mason, who's averaging 5.6 yards per carry this season. It seems obvious that Mason should be head of Mitchell, but isn't. And when I asked Kyle Shanahan why last week, Shanahan simply said that Mitchell has done some good things for the 49ers in the past, which is true.

So when it was time to give McCaffrey a breather this past Sunday against the Buccaneers, Mitchell replaced him, rushed four times and gained 24 yards. It was his first good performance of the season. Finally, he looked healthy and explosive. And it became clear why Shanahan prefers him to Mason.

Mitchell is a better fit in the 49ers' current offensive scheme than Mason. Mitchell can run the outside zone runs and the crack tosses and all the plays to the perimeter that Shanahan calls for McCaffrey. Meaning Shanahan doesn't have to change anything schematically for Mitchell.

Mason is a completely different style of runner. He's a big, powerful back, not a speedy scatback like Mitchell and McCaffrey. Mason isn't the best fit for outside zone runs and tosses. He's a better fit for inside zone runs and power runs between the tackles. And that's not what the 49ers generally do with Brock Purdy at quarterback.

Mason is a holdover from the Trey Lance Era, when Shanahan envisioned running the zone read and having the running back dive between the tackles. That's what Mason was for. But now Lance is gone, and so Mason has become a spectator, even though statistically he's outstanding. 

Life can be so unfair.