Raheem Mostert or Trey Sermon: Which 49ers RB should I start?

Should you start Raheem Mostert or Trey Sermon in Week 1 of the fantasy season, or should you be looking to avoid both 49ers RBs this week?

The debate between which San Francisco 49ers RB out of Raheem Mostert or Trey Sermon fantasy football managers should lean on in Week 1 has been building since Sermon was drafted in the third round back in April. Ahead of the first week of the fantasy season, what is the outlook for both Mostert and Sermon, and can you rely on either 49ers RB this week?

Update 9/12/21: Trey Sermon has been announced as inactive by the San Francisco 49ers. This cements Raheem Mostert as the RB1 in this backfield.

Raheem Mostert is ahead of Trey Sermon on the 49ers’ RB depth chart

Make of this what you will, but it is hardly a surprise the veteran (Mostert) is ahead of the rookie (Sermon) on the 49ers’ RB depth chart. The 49ers recommitted to Mostert financially, and he has performed for them when given the opportunity.

Over the past two seasons, Mostert has racked up 1,293 rushing yards on just 241 carries. That is an impressive average of 5.4 yards per attempt for the 49ers RB. However, injuries have ensured that Mostert has not really demonstrated just how good he truly can be.

Meanwhile, Sermon is coming off a 116-carry, 870-yard rushing season with Ohio State in 2020. However, Sermon rushed for 636 of those yards in a three-game span. He is certainly explosive, but there are question marks about how much workload he can handle after being injured on the first carry of the game against Alabama to end his college career.

The 49ers appear to have a soft matchup in the Lions

There is only so much you can read into last year’s stats, given the Lions have a brand new coaching staff. However, other than the addition of Michael Brockers, they did not add anyone who immediately makes you think their run defense will be significantly better. That should be good news for Mostert and Sermon.

Last season, the Lions were the worst team in the league against RBs, per NFL.com. The Lions allowed 31.99 points per game, 1,855 rushing yards at 4.6 yards per attempt, and 19 touchdowns on the ground. They also allowed opposing backs to rack up 770 receiving yards and 10 touchdowns. That all equates to 164 yards and 1.8 touchdowns per game to the RB position.

Should you start Mostert or Sermon in Week 1 of the fantasy season?

Let’s start by acknowledging that the presence of both Sermon and Mostert severely limits the other’s upside. However, if there were a matchup where both could succeed, it would be this one.

If they were to split the work evenly in Week 1, the stats from 2020 tell us you’d have around 15-16 fantasy points in Week 1. In 2020, averaging 15 fantasy points per game would have been enough to rank eighth at the position over the course of the season.

Now, the chances they perfectly split the work is meager. But, with this matchup, both have the potential to be RB2 options at least.

Ben Rolfe is a Senior Managing Editor at Pro Football Network and is also a member of the Fantasy Sports Writers Association (FSWA). You can find him on Twitter @BenRolfePFN.