It’s rare that a rookie is able to come in and hold his own against the grown men around the NBA immediately. But it’s almost unprecedented for an NBA rookie to outperform every player in the league as soon as the season tips off.

That’s what Jayson Tatum is doing from the three-point line this season.

Tatum is shooting 51 percent from three-point range for the Celtics. When he got off to a hot start early this year, most people thought he’d cool off. But we’re nearly a quarter of the way through the NBA season and the rookie has shown no signs of slowing down.

The percentages say there’s not a better three-point shooter in the league than Tatum right now and he’s probably the player people least expected to be in the category — but here we are.

Let’s crunch the numbers a bit.

Tatum is shattering rookie shooting records right now

The last rookie who accomplished that in a season was Anthony Morrow in 2008-09 with the Warriors. And Morrow got up his shots, but he only took 2.7 threes per game compared to Tatum’s 3.0. Morrow also only made 47 percent of them while Tatum is knocking down 51 percent of his threes.

The Celtics rookie is in rare company as a rookie shooting with a money jump shot. He’s one of four rookies ever to shoot at least 45 percent from three on at least two three-point attempts per game with 400 minutes played. He’s shooting the best percentage ever as a rookie with at least two three-point attempts taken while playing at least 20 minutes per game — and that list is long and filled with great shooters.

But it’s not just the rookies Tatum is outplaying

It’s the veterans, too! From the past and present. Tatum is shooting the ball at a historically great clip. He’s one of six players in the league’s history to shoot 50 percent from deep while taking at least two three-point attempts per game and playing at least 400 minutes in a season.

The other players on that list include legendary shooters like Steve Kerr, Tim Legler, Detlef Schrempf, and Kyle Korver. And only Legler and Jason Kapono took more three-point attempts than Tatum did in those seasons.

Need more perspective? Tatum is only 19 years old. No one else on that list is younger than 25 years old. The Celtics rookie hasn’t even hit his stride yet.

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No one expected Tatum to be this good

Tatum only shot 34 percent from deep at the college level and was never really considered a great spot-up shooter. His most attractive skill seemed to be his ability to make plays in isolation.

In fact, Mike Schmitz of Draft Express considered Tatum’s three-point shooting a “swing skill” in his scouting report of the young forward in June.

Tatum's swing skill is his 3-point shooting, an area where he showed promise throughout the year - namely a 6-of-7 game versus Virginia that featured two deep hang dribble pull-ups that he hadn't shown otherwise during the season. If he's able to step out and turn into a reliable 3-point threat, and a more instinctual ball-mover, he has the chance to become much more versatile in his already polished scoring attack.

Tatum showed he had potential as a shooter, but no one expected him to actualize it this quickly and this effectively. When you couple that with his ability as a scorer, he’s a dangerous offensive player. It’s why he’s been so dependable for the team with the best record in the league so far this season.

Tatum might not be the best shooter in the league, but he’s still been effective

I know what you’re thinking: Volume has to matter. In today’s NBA, three three-pointers per game isn’t a lot. But when you’re hitting 51 percent of them? That becomes a perfect number for a highly effective shot.

Tatum’s usage rate is only 17.7 percent and he only takes 9.1 shots per game. That means about a third of his shots are coming from deep and they’re mostly of the spot-up variety. He’s making about 1.5 of those attempts from deep, which translates to about 4.6 points per game for Tatum before we even start to talk about his effectiveness from mid-range and inside.

He’s scoring 1.17 points per possession per game on spot-up attempts, per NBA.com’s stats tool. That puts him in the 76th percentile of all NBA players on spot-up attempts as a rookie. As the Celtics’ fourth option, he’s a guaranteed bucket.

For Tatum, less is more. And he’s doing a lot more with what he has than most players are doing with volume at 19 years old. Will he slow down? Maybe. But who cares? What he’s doing is impressive and we should look forward to watching him grow instead of waiting for him to fold.

Boston's dynamic duo of Jayson Tatum and Jaylen Brown