Dereck Lively II, Dallas Mavericks (surpassed expectations)
Dereck Lively II will be a little bit easier to explain his inclusion on this list. While other rookies such as Detroit Pistons' Ausar Thompson, Oklahoma City Thunder's Cason Wallace, and New Orleans Pelicans' Jordan Hawkins do deserve consideration for this spot, none of the aforementioned rookies start for a team that currently leads their respective division.
Out of the 23 games Lively II has played, he has started in 22 of them. To me, this is what separates Lively II from the others. In a draft analysis by RotoWire, featured on NBA.com, "Longer term, he could develop into a starter, especially if he blocks shots as expected and finds a point guard with great touch throwing alley-oops."
Well, suffice to say that he is already a starter and he's only going to get better as he gets more reps. His glamour stats won't wow you, 8.9PPG, 7.7 RPG, 1.1 APG, 1.6 BPG, but those are solid numbers for a rookie center who might eventually become a starter.
The crazier numbers are when you investigate a little further and see that his field goal percentage sits at 73.4%, and his true shooting percentage is 72.8%, which is almost 15% higher than the league average. Free throws will be something that he'll need to work on in order to be more reliable for late-game scenarios, but it has been an incredible start to Lively II's career, and he is miles ahead of where expectations had put him.