What is going on in the NBA? Why all the trouble with fans, now that the playoffs are here? What is going on?

A fan spitting on a Atlanta’s Trae Young. Another chucking a water bottle (it missed) at Brooklyn’s Kyrie Irving as the Nets player tried to reach the lockerroom. A third who dumped a bag of popcorn on the head of Washington’s Russell Westbrook — while a game was in progress.

Then, last night, a miscreant took it to the next level when he maneuvered his way onto the court, in Philadelphia, before he was taken down by security.

All of these incursions have come in the past few weeks. Most NBA fans are glad the playoffs are back in public view, but a fringe group of idiots is making life difficult.

Here is what should be done immediately.

–Beef up security personnel at all games, certainly for the duration of this season’s playoffs. Off the top of my head, I’d say triple the number of security personal. A league as wealthy as the NBA can afford it. The guy at the end of the bench would cost more than the additional security folks.

–For those who might be thinking of something even more invasive, send fans through a metal detector before they can enter the arena. (We have reached that point. Yes.)

–Diagnose hot-spots around the court. Early on, these can be spotted before contact with players begins. The over-loud, the obviously drunk. Escort them out immediately.

—Make lists of bad actors. Post them in the stands and the entrance and exits, with a big color photographs to be posted throughout the area,

This stuff is no fun, but it is necessary. If/when some sense of decorum returns, maybe we reduce the security precautions. But don’t do it any time soon, not as long as players are being attacked.

Back in the 1990s, baseball had a weird period when fans fairly often would run out on the field to do … whatever. Shake a player’s hand. Live up to a drunk friend’s dare. Run around for a while until people with badges brought them down.

I talked to Dodgers outfielder Brett Butler about this, and he said players are afraid of fans who enter the playing area — because they do not know if this particular invader is the one who will commit serious violence. He said: “First thing I do is look at their hands. Are they carrying anything dangerous? That’s what I think about first.”

NBA players and security must be feeling that way about now. “Is that fan carrying a weapon?” That must be just plain scary.

Looking ahead, the NBA must consider reconfiguring their arenas. It seems clear the game has to create a barrier between players, coaches, game officials — everyone who is sitting on the lowest level of the arena.

The barrier might look something like the plexiglass that surrounds National Hockey League games. Big spenders won’t be able to chat with players, as they do now, but they will be only 10 feet, maybe, further from the action.

Currently, NBA players practically have to walk through the crowd in the narrow area that leads to the lockerrooms. That should not be, no matter how much some fans are willing to pay for the astonishingly intimate court-side seats.

A big factor in whatever this is about is verbal. People saying things they would never say in mixed company. Verbal filth heaped on the players should not be allowed. Those who speak that way should be promptly led out of the arena.

Let the players play. Let them concentrate on their elite competition. They are trying to please you with their skills and strength. Let them be able to focus on their jobs between the lines.