The commercial is … modest. That might be the best word for it.

Along with his other obligations during All-Star Weekend in Los Angeles in February, Jayson Tatum filmed a spot for Metro PCS. The midtier wireless carrier’s profile is similar to Tatum’s, in a way. It’s national, but the T-Mobile subsidiary gets far less attention than behemoths like AT&T, Verizon, or Ben Simmons.

The NBA Playoffs Check out The Ringer’s coverage of the 2018 NBA playoffs

It’s Tatum in a gym, with basic Nike sweats on and a ball in his hands. He does some nifty dribbling, almost definitely travels, and makes a lefty layup. Then he turns around and … there’s no one else there but the dude sweeping the floor.

Cut to a smartphone, through which his longtime trainer, Drew Hanlen, is watching remotely and offering feedback (including to put more “sauce” on the move). “It’d be a rookie move for me not to train as hard as I can,” Tatum says in voice-over. “But it’s also important for me to put in the right work. That’s why I have to stay connected with my coach, even when he’s not around.” It’s a funny premise, one that, it turns out, stems from real life.

At one point before Tatum’s senior year in high school, the pair was working on revamping his shot when Hanlen was called away by other clients for an extended period. So Tatum would hit the gym with Hanlen’s videographer, Sam Limon, and loop the trainer in via smartphone. “They would FaceTime me and say, ‘Hey, are we doing this right? Are we doing this right?’” Hanlen says.

The theme of the commercial is rookie moves, which is something of an odd fit since the 20-year-old doesn’t often make rookie moves. Tatum’s season has reached a point that, after he scored a team-high 21 points against Philly to help lead Boston back from a 22-point deficit to take a 2-0 series lead in Game 2, reporters at TD Garden wanted to ask about Simmons’s bad night. Not about how Tatum had put together another astonishing performance, or how he’d just tied Larry Bird’s Celtics record with four straight 20-plus-point postseason games as a rookie.

That, by now, is old news. Especially because with two more 20-plus-point games in Philadelphia and a 25-point outburst in the Celtics’ 114-112 Game 5 win that clinched the second-round series on Wednesday, Tatum now holds that record all by himself.

Jayson Tatum’s been around basketball since the day he was brought home from the hospital, when his father, Justin, slipped a Nerf basketball into the infant’s crib.

“I just knew that was gonna be our niche, our bond,” Justin Tatum says. “Having him at such a young age, we maybe can’t say we were the best father and mother, but I found my way to connect to him through the game of basketball.”

As a toddler, Jayson was on the sidelines for his father’s college home games at Saint Louis University. After a brief stint playing pro overseas, Justin returned to St. Louis to work and to coach his son, focusing on fundamentals: developing his off hand, learning proper footwork, and only then working on shooting.

Justin knew early on, when Jayson was in the second or third grade, that his son was different. Other kids in the YMCA league would grab a rebound and wait for everyone else to run back on defense, then dribble up the court.

“Not with him,” Justin says. “He got the rebound, pushed it by everybody else, and laid it in. People would say, ‘He can’t be the same age as everyone else. How does he know to do those things?’

“Whenever I went to the gym, he was with me. So he had a better understanding than those kids who practiced once a week. He had that aggression from the jump.”

“He would love to have that rein to say, ‘Everybody get out of the way.’ He wants to do it [now]. But he understands there’s always a process. You don’t know the type of talent, the type of hunger that’s being contained right now.” —Justin Tatum, Jayson’s father

That competitive drive manifested itself in weekends spent at AAU tournaments instead of goofing off with friends, and in 6 a.m. workouts before class in high school and evening workouts after practice. And it doesn’t stop, no matter whom he’s going up against.

When Jayson was a freshman at Chaminade College Prep, Justin got the head-coaching position four miles away at Christian Brothers College High School, his alma mater. Many assumed that Jayson would transfer from one rival to the other to play for his father. But Jayson and his mom, Brandy Cole, had other ideas. He stayed. And instead played against his father’s team twice a year. Those Tatum-vs.-Tatum matchups, as they became known locally, got so big that eventually the teams were forced to move them to a nearby Division II college gym.

“I told a lot of my kids, ‘A lot of you won’t play in a game like this, with a crowd like this, again. Take advantage of this,’” Justin says. “I put enough gas on ’em to think we were gonna win. But in the back of my mind, I thought, ‘It’s gonna be tough to get by this team.’”

He was right more often than not; Jayson finished with a 5-1 record against CBC (quoth the father, laughing: “I’m so happy he’s gone”). When the two teams faced off, Justin would instruct his players not to trash-talk Jayson—not because he wanted to protect his son’s feelings, but because the smack talk just fired him up even more.

That kibosh on trash talk didn’t necessarily go both ways, though, as Jayson would occasionally sidle up to Justin and, if he was having a good scoring night, tell him to put someone else on him on defense. Those moments were rare breaks from the younger Tatum’s single-minded focus.

“He went into a huddle, down four to us,” Justin says of one matchup. “He ran in the huddle and told everybody in the huddle, ‘Nobody else take a shot. I’m gonna finish this game.’”

Just a few years later, Jayson’s champing at the bit to get that opportunity in Boston.

“He would love to have that rein to say, ‘Everybody get out of the way,’” his father says. “He wants to do it [now]. But he understands there’s always a process. You don’t know the type of talent, the type of hunger that’s being contained right now.”

Perhaps the only rookie move in Tatum’s portfolio came six years before he was an NBA rookie. It’s the recently rediscovered beckoning tweet he sent LeBron James’s way:

@KingJames Follow back it's Larry Hughes nephew from st. Louis and Abe and Rj Lil cousin and Justin Son Follow Back pic.twitter.com/AnOnb7E8 — Jayson Tatum (@jaytatum0) April 13, 2012

When he sent that tweet, Tatum had been sweating with Hanlen for about a year, having convinced the trainer he had what it takes to cut it in workouts designed for NBA players like David Lee and Bradley Beal (who both went to Chaminade before Tatum).

“The first couple workouts that I ever had him ... I really pushed him to an extreme level,” Hanlen says. “Just to see if I could bitch him out, for lack of a better term. And while he was exhausted, while he was really tired, he always kept battling through the workout and kept coming back for more.”

With Tatum having proved his dedication, the pair got down to the nitty-gritty immediately with a week of jab-step work. Tatum’s favorite player, Kobe, served a dual role as the inspiration and the study material.

“As a 13-year-old, to not be shooting jump shots, not be working on a bunch of one-on-one moves, not be working on a bunch of dribbling drills that might look cool on social media,” Hanlen says, “for him to be sitting in the gym and for a week straight, [doing] two-a-days of just jab work, it just shows you how he handled himself as a young kid.”

All the behind-the-scenes work Tatum’s put in, all the reps in the empty gyms, all the film study and FaceTime sessions—Hanlen says that the rookie dialed him up after putting up 21 points in Game 2 of the Philly series for pointers on his 3-point form—convinced Hanlen of not only Tatum’s bright future, but also his great present.

“I have a lot of clients in the NBA,” the trainer says, “that range from All-Stars to starters and this and that, and I think he’s one of the most skilled players in the NBA now.”

He’s put those skills on display in the postseason, averaging 18.8 points, 4.5 rebounds, and 3.2 assists a game and shooting a couple of ticks below 50 percent overall. Against Philly on Wednesday night, he became the third player 20 or younger to score 25 points or more in a clinching playoff game (the others: Magic Johnson and Tony Parker). And that’s not the only way he’s scored a spot next to Magic in the history books, becoming one of just five players in NBA history to crack 200 postseason points at 20 or younger:

Tatum Among Rookie Postseason Scoring Leaders Player Year(s) Games Points Player Year(s) Games Points Kobe Bryant 1997-99 28 328 Tony Parker 2002-03 22 325 Magic Johnson 1980 16 293 Jayson Tatum 2018 12 226 Bradley Beal 2014 11 211

The last two of his 25 points helped push the Celtics past the Sixers into a matchup with the Cavs in the Eastern Conference finals. Tied at 109 with less than a shot clock left to play, Tatum cut through the lane. Marcus Smart fired a skip pass his way, but the ball drifted behind the rookie and toward T.J. McConnell. Tatum, like a wideout in traffic, reversed his momentum and snatched the ball out of the air, despite a collision with the Philly point guard. Then, when no whistle blew, he quickly gathered himself and made the layup for a two-point lead.

JAYSON TATUM FOR THE LEAD pic.twitter.com/ia6eIV1eb3 — Boston Celtics (@celtics) May 10, 2018

The Celtics didn’t trail again.

“It’s a great feeling,” Tatum said of teammates looking his way in big moments. “You work all season to earn the trust of your teammates and coaching staff for moments like this, and you’ve just gotta go out there and make the right play, whether it’s finding Al [Horford] on the lob or me scoring a layup. We’re just trying to make the right play.”

Now that they’ve defeated the heavily favored Sixers—without stars Gordon Hayward and Kyrie Irving and with Smart still banged up, Jaylen Brown dealing with a hamstring injury, and even Tatum wearing a wrap on his jammed left hand in the second half Wednesday—the East’s no. 2 seed will host James, Kevin Love, and Kyle Korver in the conference finals. Boston will be the underdog in that series, too, home-court advantage (the Celtics are undefeated at home in the 2017-18 postseason to date) be damned.

If they’re going to have any chance of beating that Cleveland squad, coming off a sweep of the top-seeded Raptors, the Celtics will need Tatum and Co. to keep performing at this record-setting level. That’s fine by Tatum, who said in a quiet moment pregame Wednesday, “I’ve always envisioned myself in big moments, ever since I was little. … It’s a dream come true. Two years ago, I was in high school.”

And now he’s here, a rookie who moves around the court like a seasoned vet, knows how to create space to get his shot off, and uses a high basketball IQ to hold his own on defense. With 20 points or more in seven straight postseason games, Tatum’s turning the increased role the injuries to his teammates has given him into a showcase, a chance for a national audience (and advertising executives) to see what Celtics fans have watched all season long.

“Jayson’s got aspirations of being an All-Star and winning championships, and he dreams of being an MVP one day,” Hanlen says. “It’s one thing to want those things and it’s another to work for those things. He’s gonna be living in the gym all year round until he accomplishes those things.”