The 49ers made a huge mistake trading this player to the Vikings

What were they thinking?

San Francisco 49ers general manager John Lynch. | Joe Nicholson-Imagn Images

For the most part, the 49ers made good moves this offseason.

They hired Robert Saleh, who might be the best defensive coordinator in the NFL. They drafted Mykel Williams, who already is playing like an elite run defender. And they traded for Bryce Huff, who has two sacks in three games. So it's no surprise that the 49ers' defense ranks has allowed the third-fewest points and fourth-fewest yards in the NFL this season.

But there's one move the 49ers made on offense this offseason that they have to regret.

The worst trade of the offseason

On March 18, the 49ers traded Jordan Mason and their sixth-round pick to the Minnesota Vikings in exchange for their fifth-round pick and a sixth-rounder next year. That's all they got in exchange for him.

And they traded Mason purely for financial reasons. He wanted a modest extension, and the 49ers wouldn't give him one. So instead, he signed two-year, $10.5 million extension with Minnesota.

Minnesota Vikings running back Jordan Mason (27). | Jeffrey Becker-Imagn Images

And now, Mason is the Vikings' starting running back, and the NFL's eighth-leading rusher with 214 yards, he's averaging 5.3 yards per carry and he has 2 touchdowns.

Meanwhile, Christian McCaffrey is averaging just 3.4 yards per carry and has no rushing touchdowns. To be fair, he's still a good receiver. But, he's not the runner he used to be. And his backup, Brian Robinson Jr., the 49ers traded for to replace Mason, is averaging 4.4 yards per carry and has 0 touchdowns.

Which means the 49ers traded away their best runner for a late pick. Granted, they spent that pick on safety Marques Sigle, who's their starting strong safety. He looks solid so far. But, the 49ers had an earlier fifth-round pick which they used on running back Jordan James. They could have spent that on Sigle instead, kept Mason and not drafted James, who has been inactive for all three games this season.

The 49ers are a good team. They have an elite defense and two good quarterbacks, which is why they're 3-0. But they can't run the ball. They're averaging just 3.3 yards per carry, down from 4.7 last season.

Arizona Cardinals linebacker Mack Wilson (2) puts the hit on San Francisco 49ers running back Christian McCaffrey (23). | Cary Edmondson-Imagn Images

Part of the issue is the blocking. They lost left guard Aaron Banks this offseason and replaced him with Ben Bartch, who's injured. The next man up is rookie Connor Colby, who didn't play well in his first career start on Sunday.

But the running backs are problems, too. Neither McCaffrey nor Robinson are explosive anymore. Neither one breaks tackles like Mason does.

In hindsight, Mason's extension was a bargain. Trading him to the Vikings was a tremendous act of kindness and charity. Sure, the 49ers may have gotten worse as a team, but they helped MInnesota improve, and that's generous.