For fantasy players who have been holding onto Peterson despite his nonexistent production, the news should come as a major relief.
While Peterson was mired in a running-back-by-committee situation in New Orleans—and was clearly third in the pecking order behind Mark Ingram and Alvin Kamara—he should instantly ascend to the top of the depth chart in Arizona, as the team has gotten minimal production from the position since David Johnson's injury.
So, is Peterson now a must-start player in fantasy football?
Let's start with the positives. Peterson is likely to see the early-down and goal-line work in Arizona, while Andre Ellington will likely remain a third-down back and threat in the passing game. Peterson should be an upgrade over Chris Johnson (2.5 yards per carry) and Arizona's running backs in general. That group has been dreadful compared to the options in New Orleans, as Nathan Jahnke of Pro Football Focus noted:
Peterson should see far more opportunities in Arizona than he did in New Orleans. That's a major positive.
The question, however, remains what Peterson will do with those touches. It's important to consider that if Peterson was still in his prime, he never would have been buried on New Orleans' depth chart behind Ingram and Kamara.
In other words, Peterson has clearly lost a step, a point Adam Levitan of DraftKings elaborated on:
But there's also the question of Arizona's offensive line. Peterson may get touches, but he's not going to do much with them if the O-line can't open holes.
Evan Silva of Rotoworld and B/R's Matt Camp aren't confident in that group:
Add it all up, and Peterson isn't a must-start for fantasy owners. Still, given the increase in touches he'll see in Arizona's offense, he does enter the flex conversation immediately and should be owned in all formats. He's likely going to be a player worthy of your flex spot in the bye weeks or when the matchup is favorable.
Otherwise, proceed with caution.