NEW YORK >> After 20 years in the NBA, Dirk Nowitzki can’t be fooled.

He knows when teams aren’t giving an honest effort, when they are out there playing but not playing to win.

“It’s pretty obvious,” Nowitzki said.

While easy to spot, tanking is not so easy to stop, the NBA is finding.

It’s a problem for the league office, which has fined owners, chastised teams and sent out league-wide memos on the topic. And with big brother watching, teams are abiding by the letter of the law, but arguably not the spirit of its intent.

Tanking is viewed as a solution — sometimes the only one — for some teams and their fans, hoping something good can come from being bad if they cash in at the lottery and land a top draft pick.

Nearly a third of the 30 NBA teams are brutally bad this season, and it’s hard to believe some aren’t losing on purpose. Phoenix, Memphis, Atlanta, Orlando, Dallas, Sacramento, Brooklyn, Chicago and New York are all on track to lose 50 or more games, and only the Nets aren’t motivated to lose — they don’t own their first-round pick.

Everyone else comes under suspicion when something strange happens:

>> What was leading scorer Dennis Schroder doing on the bench for the entire fourth quarter of Atlanta’s one-point victory over Phoenix on March 4?

>> Why did Tyreke Evans foul Chicago rookie Antonio Blakeney attempting a 3-pointer with 1.8 seconds left and Memphis leading Chicago by one?

>> Are some of these guys on injury lists really hurt?

New York hosted its own version of March Badness over the last week, with the Knicks and Nets both playing Nowitzki’s Mavericks, before Memphis and Chicago came to the city on the same sad Monday. That’s five of the nine bottom teams — including the only two known to have been contacted by the league office because of their tactics.

Here’s how it looks where currently winning really doesn’t seem to be everything:

CUBAN “MESSED THAT UP”

Tanking is a discussion for fans and media. Nobody from a team ever dares talk about losing on purpose.

Except Mark Cuban.

When the Dallas owner went on Hall of Famer Julius Erving’s podcast in February and said he told his players that “losing is our best option,” the league fined him $600,000 for “public statements detrimental to the NBA.”

That put a spotlight on the Mavericks. So if they were planning on packing it in and trying to add more young legs in the draft for Nowitzki’s expected swan song, they had to change plans.

“Well, I think Mark messed that up for us,” Nowitzki said, with a straight face.

They went on a recent stretch of three wins in four games — two were against the Grizzlies and Knicks — and Nowitzki insists that teams are still tanking despite the league’s mandate.

“There’s obviously some teams that are going for some losses now, and we’re one of the teams that still wants to win and we’ll see where we end up at the end in the draft,” he said. “But we’re still playing. We want to have a winning culture for our young guys.”

JUST THAT BAD?

If the Knicks are tanking, they are being out-tanked.

New York went 1-16 in a recent 17-game stretch, managing only to beat fellow lottery-bound Orlando, in a freefall that should’ve been able to take the Knicks close to the bottom. Instead, they remarkably remain the best of the worst, remaining ahead of the other eight in the standings — which means, behind them in lottery odds.

With Kristaps Porzingis lost to a torn ACL last month and Carmelo Anthony traded in the offseason, the Knicks don’t have the talent to win often. But coach Jeff Hornacek believes there’s a reason the other bad teams can’t win, either.

“The top teams are always there but I think that middle group, teams that are seeded in the playoffs 7, 8, guys that are just outside that, those are some pretty good teams nowadays,” Hornacek said. “So if you are one of those bottom teams, you used to be able to beat those teams occasionally. Now it’s tough to beat those guys, too.”

INJURIES & TANKING

Chicago came to New York on Monday night without Zach LaVine, Lauri Markkanen and Kris Dunn, its three top scorers. Bulls coach Fred Hoiberg said they were all hurt, and people down the street at the league office were likely wondering.

When the Bulls stopped playing starters Robin Lopez and Justin Holiday earlier this season, the league reminded them of the new resting rules, which allow Commissioner Adam Silver to fine teams who sit multiple healthy starters in road games.

So the Bulls started playing Lopez and Holiday again — sort of.

They went the whole first quarter at Detroit on March 9, combining for 15 points as the Bulls led by five. Neither got off the bench again, and the Pistons outscored them by 21 the rest of the way.

But Hoiberg wasn’t worried about creating any further trouble by playing without the three players acquired in the Jimmy Butler trade with Minnesota last summer. He insists they were injured.

“When they’re ready to go,” Hoiberg said, “they’re going to be back out there playing again.”

FANS’ TAKE

A matchup of 24-45 vs. 25-45 is often one to avoid, but longtime Chicago fan Louis Rodriguez was thrilled to catch Bulls-Knicks. He’s just not used to seeing his favorite team attempt to lose.

“The Bulls franchise is a legendary franchise and it won’t be the last time we see them No. 1,” he said.

Dressed in his Bulls shirt and red hat, he came from Naugatuck, Connecticut, with his stepsister Shannon Bahme, who was wearing a Knicks shirt.

The Knicks have been losing for years, so it’s easier for their fans to accept being bad. Some remember three years ago, when back-to-back victories in the final week of a 17-win season knocked them out of pole position in the lottery. Minnesota beat them by a game for the worst record, then won the lottery and the right to draft All-Star Karl-Anthony Towns.

So are the Knicks tanking?

“I think they’re losing on purpose,” Bahme said. “They’ve got to be. I mean, you can’t play that bad. Hornacek … just puts in people that do not belong in.”

THE YOUNG AND THE RESTING

Tyreke Evans is Memphis’ leading scorer, a former Rookie of the Year who has recovered from injuries to regain his old form.

Yet Monday — in the game after snapping a 19-game losing streak — the Grizzlies sat him out for longer looks at Andrew Harrison and Briante Weber. Oh, and Marc Gasol was also out with the flu.

Coaches argue that’s not tanking, but merely development and evaluation of younger players. Harrison took a contested 3-pointer for a final shot that wasn’t close in a 118-115 loss to Brooklyn.

He took the blame, but coach J.B. Bickerstaff indicated he’ll get more chances.

“It’s learning how to win. And consistency and learning how to win are the two hardest things to develop in this league,” he said. “So the only way you learn is through experience in these situations.”