I've been watching a fair bit of Williams over the past couple of days and I have some thoughts.
The one trait that sticks out to me more than anything else is ability to gear up in a blink when he sees the hole. He isn't going to create a lot on his own, but he's fairly patient and when he sees the crease he can get up to speed exceptionally fast. In that sense he does have a "2nd gear" though he doesn't have runaway long speed.
What everyone knows about him is that he's a violent runner who gains a lot of yards after contact. He also displays a functional jump cut to elude defenders at times. But aside from that, he isn't especially elusive. His game is about hitting the hole really hard and daring you to tackle him. I like that as a complimentary facet of a backfield.
But what I think got him drafted over other RB options is his pass protection. He isn't Ezekiel Elliott in that regard, but he's pretty darn good for a college back. And more than just being able to body guys up, he has the ability to identify the free rusher and get himself squared in time to do something about it. That skill set escapes a lot of young backs. Also, as a somewhat irrelevant side note, if he ever ends up in the position to block for a teammate trying to advance the ball, he goes after it with a lot of gusto. Obviously that isn't an important part of RB evaluation, but in general he's fun to watch because he plays with a lot of energy and hustle.
He was not a prolific receiver for BYU, but after watching quite a bit of him I think he could have been more of one. The issue was that Taysom Hill's version of the "check down" was to take off. There were many plays where most QB's would have hit the back, but Hill rather trusted his legs (side note-- Taysom Hill fumbles a lot). When Williams was targeted, he demonstrated pretty reliable hands. Speaking of reliability-- I do like that he rarely fumbles. He had two fumbles on 234 carries last season. Losing the ball once every 117 times you touch the ball is pretty fine work. For comparison, Fournette fumbled once every 43 carries last season, while Dalvin Cook fumbled once every 48.
My main concern with him is whether or not his power, his most relied upon skill set, will translate to the NFL. He's a 6'0' 212 lb back who made a living in college by being explosive in a straight line and gaining yards after contact. Are NFL defenders going to be able to get him on the ground more consistently? Is a 212 lb back going to be an effective grinder like that? I'm really unsure. It's interesting that the perception is of Williams as a big back and Jones as a small guy. Jones is 208 lbs, a mere 4 pounds lighter, despite being 3" shorter.
I would say his ceiling is as a slashing power element to lead a RB committee, and his floor is as a complimentary player who specialized in pass protection. We will see where he lands on that spectrum.
