Grant Williams got into a 3-point shooting contest with Jayson Tatum on Wednesday and lost, which carried the penalty of push-ups. The rookie forward gladly complied.

But Tatum, claiming that Williams still owed him 10 more, turned to guerilla warfare yesterday. When Williams reemerged after a video session with Celtics assistant coach Alex Barlow, Tatum pointed to the floor and demanded five.

The rookie sat down for a media interview, only to hear a shout from Tatum to shut up. He moved on to another interview, and this time Tatum reappeared to demand his remaining five push-ups.

“Jay has got me a couple of times. I owe him a couple, but it keeps me going,” Williams Thursday at the Auerbach Center. “Push-ups, I’m good. Nothing crazy. We’re young guys who love making each other look embarrassed. Mid-interview he’ll ask me to do five push-ups. So I have no idea when to expect it. So I’m on my toes at all times.”

He probably didn’t need the aid of impending punishment to remain alert in his first NBA training camp, but as expected, Williams has approached it all with his usual mix of confidence and openness to whatever comes his way.

He was the leader on a tournament-tested University of Tennessee team, and whenever possible, Williams has continued to step forward this week. Some rookies are subdued in their first week alongside NBA veterans. That’s not Williams.

“That would not be the first word I would use to describe Grant,” said Brad Stevens. “He is not a subdued guy and that’s good. You want all these guys to feel comfortable being themselves, lending their thoughts and working together. He has a bright future. He’s going to be an NBA player for a long, long time. He’s really smart.”

Williams, too, has longevity in mind. As a player of high basketball IQ and a great overall grasp of the game, he can also see himself in the picture for a significant amount of time.

He chose an interesting player to study prior to the NBA draft – then-Celtic Al Horford, whose game gave Williams an important introduction into what it would take to fit into Stevens’ system.

“Al’s just a talented player. Watching him was about how he fit in Boston, and also the things that he got, because the NBA is about a lot of different defenses that play you different ways, and Al has pretty much adjusted throughout the entire time,” said Williams.

“Watching guys like him, watching guys like Paul Millsap, watching guys around the league who have been here for awhile, that’s what you hope to do, play a long time.

“Not five years. You hope to play 17. I love watching film of other players, good to give them recognition occasionally, but you also know you’re going to war any time you see them.”

To get that far in today’s NBA, Williams will have to work on his versatility. It’s a good idea to get into 3-point contests with Tatum, because that shot in particular will make Williams a serious threat.

He often had the ball in his hands at Tennessee, and playmaking, another Horford skill, will help Williams in his quest for early career minutes.

“You have to learn every position just in case you’re asked to play it,” he said. “That’s just how I view basketball. But the biggest thing for me is to make other people’s jobs easier. My thing isn’t to go out and do things that are crazy, or try to make impressive plays. My things will probably go unnoticed, and that’s the way it should be. That’s the way you prefer it. They can get you open shots, and you can get them open shots as well.

“Just work through the offense,” said Williams. “It’s a flow-based offense and you really just have to make the right reads, and that’s where playmaking comes out. It’s not going to be like at Tennessee where I had the ball in my hands all the time. We have a lot of guys who can play with the ball in their hands. It’s more so about using your knowledge, whether it’s a screen that you set, or seeing something ahead and calling it out for somebody else who has the ball in their hands. Getting a rebound and hitting somebody up the court. That’s where the playmaking will come in.”

Three days into training camp, Williams certainly appears to have a well-defined path.

“It’s really good,” Stevens said of the rookie’s basketball IQ. “Like any other young player he has a lot to learn about the NBA, the night-in, night-out challenges and all that comes with playing each team. As far as coming in and doing things and picking things up quick, from a strategy standpoint and also from an intuitive standpoint, he’s pretty impressive.”