DENVER - Robert Williams has played 465 minutes of NBA basketball so far in his short career.

Kemba Walker has played 473 this season.

This is important to remember. He is talented with special athletic gifts, but the talent is still raw, and he’s still just 22-years-old.

Despite all that, the Boston Celtics are relying on Williams to be one of their answers at center this season. Their piecemeal approach to the five spot is largely dependent on matchups, and Williams is getting his fair share of opportunities when those matchups are right.

The Celtics need Williams to be an effective rim defender, a good pick-setter, and a strong roller to the rim. Offensively, Williams has delivered nicely. According to Cleaning The Glass, the Boston offense is 12 points better per 100 possessions with Williams on the floor. He’s been very good in dribble handoff and high-post situations, rarely stalling the offense and often making the right pass. Even if he doesn’t get the ball to finish a play, he’s kept the ball moving, which is just as important.

Defensively, though, Williams has had some problems. Boston’s defense gives up 14.6 more points per 100 possessions and teams shoot 4.6 percent better with Williams on the floor.

“I feel like I’ve been slacking a little bit. I feel like I haven’t delivered for my team," Williams told MassLive. "I feel like I’m missing areas where I should be, a couple help side times, knowing when to stay down, going for steals. I feel like I’m making simple mistakes that I gotta tighten up on.”

Staying down is the most obvious improvement Williams has to make. So many of the breakdowns with Williams on the floor begin with him leaving his feet. This play in Phoenix might be the best encapsulation of the problem.

Robert Williams jumps on a fake by Aron Baynes

Williams biting on the Baynes fake to allow a baseline drive and dish is about as inexcusable as defensive mistakes get. To his credit, he has gotten better at minimizing these mistakes, but they still happen too often.

“We all know Rob is the jumper," Marcus Smart told me at team shoot around at the Pepsi Center. “His development to be able to stay down and guard guards off the switches or veers, and really keep them in front and really contain those guys and make it hard for them has come a long way... he knows he still has stuff to work on on the defensive end.”

Smart and the Celtics are doing their part to encourage Williams. No one claims that he is anything near a finished product, so the focus isn’t on what his doing wrong, but that he’s getting more things right.

“It’s really improving," Brad Stevens said of Williams’ defense. "He’s doing a great job of picking things up. We’re guarding different ways. We’ve guarded pick and rolls on this trip three different ways already, and he’s done a pretty good job in all those games. So we just have to keep going with that. I think he’s a really important part of the growth of our team as we forward through this season.”

He has, indeed, had his good defensive moments. He was solid against the Los Angeles Clippers, and he made some good fundamental plays in big moments.

Robert Williams defends Paul George

He slid his feet well to keep Paul George in front of him, he took the drive square in his chest, and he stayed vertical without trying to do too much. It’s a fundamentally sound play, and he’s had plenty of these this season as well. Eventually, Williams will have to string more of these plays together.

“The year’s a roller coaster," Williams said. "Everybody has ups and downs. I feel like we gotta tighten up the defense as a whole team... The focus for me is be as aggressive as possible on defense. Don’t be afraid to make calls. The guards are going to honor my calls as far as pick and rolls. Just give it 100 percent effort.”

Any lack of effort might come from on-court moments of doubt. Williams is refreshingly honest when it comes to his self-assessments, which his teammates think is a good thing.

“That just shows he gets it, he wants to be good, he wants to be great," Smart said. "For us to help him, just keep talking to him... when we get switched onto those guards, where to send his help, where his help is, what those guys want to do, stay down on those shot fakes, things like that.”

Williams has admitted to taking that doubt onto the court with him. His worst stretches seem to involve significant mental lapses, but the Celtics are patient with their young big man. They may be even more patient than he is with himself. Part of that is guys being good teammates, and part of it is the understanding that Williams is essential to this team’s success.

“He wants to do so well, and he knows his job is to protect the rim so if he feels like he’s not doing it, then he feels like he’s failed,” Smart said. "That’s not the case, but it’s a good mentality for him to have because he’s not going to get content and he’s going to continue to grow. But yeah he definitely gets in his own head sometimes just like every last one of us do, that’s why you have a group of guys, teammates, to help you come along and get out of your own head and keep going.”

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