The Boston Celtics host the Washington Wizards in Game 1 of an Eastern Conference semifinal series on Sunday at TD Garden (ABC, 1 p.m.) The two teams split their regular-season series 2-2 but it was the way that tempers tended to flare that makes this playoff rematch that much more intriguing.

Recent meetings have featured flagrant fouls, nose bops, a police presence and one team wearing all-black funeral attire. Here's an FAQ to help explain how Celtics-Wizards has emerged as the NBA's most chippy and unexpected rivalry.

How exactly did all of this start?

The dustups date to last season. In the teams' third meeting, in mid-January 2016, Jae Crowder -- perhaps the central protagonist in this entire drama -- got tagged with a technical foul in the final minute of Boston's 119-117 win in Washington. Crowder could be seen barking at the Wizards' bench and pointing at then-coach Randy Wittman. After the game, Crowder suggested Wittman cursed at him and called him soft. "[Wittman] was saying something about me being soft, and bleep, bleep, bleep," Crowder said. "I feel like he was getting away with a lot of curse words and inappropriate words to me, and I retaliated and I got hit [with the technical]." Wittman later admitted he yelled at Crowder but denied using profanity. There was no obvious escalation when the teams met again two weeks later -- a lopsided Boston win -- and Wittman was fired after the season.

With Wittman out of the picture, why didn't this whole thing just go away?

The Wizards and Celtics reportedly were two of the primary suitors for Al Horford when free agency opened in July. Boston ultimately won that tug-of-war, signing Horford to a four-year, $113 million contract. While discussing Boston's big-splash signing in August, Crowder pointed out how Boston had beaten Washington four times during the 2015-16 season and suggested the Wizards were a less attractive option because of that. At least one Wizard, Marcin Gortat, took note of the jab on social media.

So things escalated from there?

Kind of. The Wizards absolutely dominated the first meeting of the season, but business picked up when -- despite being up 20 with 5:24 to play -- John Wall clubbed Marcus Smart in the backcourt, earning a flagrant foul 2 and automatic ejection. Smart, taken to the ground by the foul, immediately sprang to his feet and exchanged words with Wall. The players were separated, but Wall appeared to tell Smart to meet him out back as the two continued shouting at each other.

So now we're cooking with gas?

The teams played nice for the first half of their next meeting in Boston on Jan. 11. But in the third quarter, Smart and Bradley Beal -- who had a bit of a history because Smart inadvertently broke Beal's nose when he hit him in the face with his off-hand going for a layup last season -- got tangled up on the baseline when Beal tried to cut without the ball. Smart and Beal exchanged words, and Beal earned a technical foul in the sequence.

Isaiah Thomas scored 20 of his game-high 38 points in the fourth quarter as the Celtics pulled away for a 117-108 triumph. After the final buzzer, Wall and Crowder exchanged words on the court near the Wizards bench, culminating with Crowder jabbing his finger into Wall's nose and Wall trying to retaliate with a slap. A herd of teammates and assistant coaches separated the players, but the teams were still yelling at each other as they returned to their locker rooms, which were in close proximity at TD Garden.

Five Boston police officers were positioned between the Celtics and Wizards locker rooms after the game to ensure no further escalation. Otto Porter suggested in the aftermath that the Celtics played dirty, to which Thomas responded, "If playing hard is dirty, then I guess we are a dirty team."

Crowder was fined $25,000 for his role; Wall earned a $15,000 penalty.

How did the teams handle the fallout from the scuffle?

The Wizards, at the behest of Beal, elected to wear all-black funeral attire to the rematch in Washington 13 days later. It was a bit of a bold decision for a late-January regular-season game, but the Wizards backed up their fashion choice with their play as Beal's 31 points keyed a 123-108 triumph.

"I wanted to win, man. I wanted to win bad," said Beal, who insisted the funeral gear was simply to inspire the Wizards.

Not only did the Celtics struggle that night, but Smart got booted from the bench after a flare-up with assistant coaches after trying to check himself back into the game despite the Wizards having pulled away.

What can we expect from this series?

When the two teams met for the final time in the regular season in late March, Boston and Washington were jockeying for position near the top of the East. It felt like there was a good chance that these teams might cross paths in the postseason. Now it’s come to fruition.

A playoff meeting should only enhance this budding rivalry. What’s remarkable is that Boston and Washington haven’t met in the postseason since the opening round of the 1984 playoffs.

Despite all the extracurriculars, it’s clear the Celtics respect the Wizards and the talent they possess, particularly in the backcourt.

"They’re a good team,” Crowder said after Boston eliminated the Bulls on Friday night. "We’ve been battling with those guys all year. Wall is their head of the snake. They’re a great transition team. I feel like we’ve got to get better and better each game with our transition defense. We’ve been talking about it [against the Bulls] as well, but it’s probably gonna be a little more enhanced with those guys, with transition and those guys getting up and down, and just try to make it a halfcourt game.”

It seems inevitable that tempers will flare in this series. The Celtics had their share of dust-ups with the Bulls in Round 1 and playing the same opponent multiple times in a two-week span leads to emotional outbursts.

This series could ultimately hinge on which team is able to best harness that energy and emotion.