1. Snaps under center
One of the reasons the San Fransisco 49ers may have liked Trey Lance over Justin Fields is that even though Fields has much more experience, Lance has actually has run more under center, play-action than Fields. That is what San Fran loves to run, so it does make sense.
It also makes sense that Matt Nagy was all about Justin Fields. He is one of the more shotgun-heavy coaches in the NFL. In fact, he had to dial it back to help Mitch Trubisky. Nagy is going to go shotgun heavy and loves that Fields is comfortable in that area.
However, Fields is going to have to grow at taking snaps under center. He took 93% of his snaps from the gun. Of that 7%, good portions were QB sneaks and kneel-downs. It was not boot-game and turning his back to the defense. Nagy is shotgun heavy but skewed in the 75-80% range. There is going to be a transition to taking snaps.
Matt Nagy even noted that commanding the huddle, is a lot different, and the line cadences, the play clock, there is a lot for Fields to grow into and learn.
Nobody is calling Fields a bust, and nobody is saying that Jared Goff, Sam Darnold, and Drew Lock deserved to have their teams pass on Fields. His upside is the best quarterback in franchise history, but there are reasons why he will not start week one, and expectations can be tempered.