Jaylen Brown #7 of the Boston Celtics drives against Pat Connaughton #5 of the Portland Trail Blazers during the 2017 Summer League on July 9, 2017 in Las Vegas, Nevada.

LAS VEGAS — NBA players under 21 can’t legally drink or go to nightclubs while in Sin City for Summer League, so Boston Celtics forward Jaylen Brown is bringing some clean fun their way on Monday night.

The second-year player confirmed to The Undefeated that he is hosting “Jaylen Brown’s Welcome to the NBA Night” at an undisclosed location. The goal of the gathering is for selected rookies and young players to bond, meet mentors and exchange ideas. Brown is paying more than $5,000 of his own money for the event, a source told The Undefeated.

“There are a lot of young guys here, and there is nothing to do in Vegas if you’re under 21,” the 20-year-old Brown told The Undefeated. “I just want to do something. Hang out, talk to them. Build relationships. I’m not 21. [Celtics teammate] Jayson [Tatum] is not 20. A lot of the draft picks are young.

“I’m going to let them bring whoever they want. Food is on me. Everything.”

Brown has commitments from the top five picks in the 2017 NBA draft to attend his party: Markelle Fultz of the Philadelphia 76ers, Lonzo Ball of the Los Angeles Lakers, Tatum, Phoenix Suns forward Josh Jackson and Sacramento Kings guard De’Aaron Fox, a source said. Other rookies include Orlando Magic forward Jonathan Isaac, Sacramento Kings center Harry Giles and forward Justin Jackson, and Charlotte Hornets guard Malik Monk. The source added that 2017 NBA Rookie of the Year Malcolm Brogdon and forward Thon Maker of the Milwaukee Bucks, Lakers forward Brandon Ingram, Suns forward Marquese Chriss, Denver Nuggets guard Jamal Murray, Dallas Mavericks guard Yogi Ferrell and Kings guard Buddy Hield are expected to attend as well. Chrysa Chin, executive vice president of strategy and development for the National Basketball Players Association (NBPA); Hall of Famer Isiah Thomas, who mentors Brown; and rapper G-Eazy also are expected to be there.

Chriss described Brown’s party as a “big deal.”

“I feel welcomed,” Chriss told The Undefeated. “He’s one of my friends. It’s just showing a leadership role with him reaching out to other players to bring them together for this event. I want to come to it just to hang out, build relationships, talk to people and enjoy myself.”

Brown was the third overall pick in the 2016 NBA draft out of the University of California. The Atlanta native averaged 6.6 points and 2.8 rebounds per game as a rookie for Boston last season while starting in 20 games. The 2017 NBA All-Rookie Second-Team selection was also in the Celtics’ rotation when they lost in five games to the Cleveland Cavaliers in the Eastern Conference finals. Brown begged to be allowed to play on the Celtics’ summer league team in Salt Lake City and Las Vegas despite it not being mandatory.

“I just wanted to play,” Brown said.

So what advice would Brown give a rookie entering the NBA now?

“One of the main things you need to know is nothing is guaranteed,” Brown said. “Fight for everything that you can. Nothing is given to you. Even if it appears given to you, it’s not. You have to scrap for everything, because there is somebody coming behind you and there is somebody in front of you.”

Brown is serving as a mentor for Tatum. They have known each other since their AAU days. Tatum has been spending lots of time working out on the court with Brown, even before summer league games. Tatum said Brown has been of “great help” so far.

“Me and Tatum go way back,” Brown said. “We played in the Elite 24 [All-Star Game] and in [Kevin Durant’s] camp. We always liked each other’s game. He was the No. 3 [draft] pick. I was the No. 3 pick. We just try to get better. I thought it was a great choice by [Celtics president] Danny [Ainge]. If we both stay around, it will be interesting to see what lies ahead in the future.

“I’m teaching him stuff I’ve seen. How to adapt quicker. I had to figure out a lot on my own last year. I had great vets, but they let me figure it out on my own. And that was fine. I figured it out. But if I had someone like myself or someone who understood it from my perspective, my learning curve would have been quicker.”

Celtics coach Brad Stevens is thankful for what Brown is doing for Tatum, who averaged 18.7 points and 9.7 rebounds during the Utah Jazz Summer League. Tatum had 27 points and 11 rebounds against the Los Angeles Lakers on Saturday in Las Vegas.

“Jaylen can help him with a lot of things,” Stevens said. “They have been in the gym a lot together. They’ve been working out together. I know Jaylen has picked him up and taken him to the practice facility a few times. Those are things that we really need. It’s important for our team. It’s about helping the next guy be the best that he can be.

“Jaylen is smart. An unselfish guy. He cares about the team. He cares about more than just what he does on the basketball court. He’s the kind of guy you want around.”

Brown, an avid Arsenal and FC Barcelona fan, has a large circle of advisers from basketball, finance, social conscience and academic fields. He also is an avid chess player, loves vegetarian food, is learning Spanish and how to play a guitar, interned with a venture capitalist while preparing for the draft, is a fan of NBA history and writes advice he receives from mentors in a journal. Hingeto, a website that enables fashion brands to crowdfund designs, is aiding Brown with starting an online hoops gear store with his own brand, a source said.

Brown has dreams of being a future president of the NBPA. The position is currently held by Houston Rockets veteran guard Chris Paul.

“That’s something that I’ve always had my eyes set on,” Brown said. “It’s a great position, and I think there is a lot of change that could still be made in the league. I don’t want to say too much … but I think I could be a great advocate for the players and represent the league well one day.”