If you want to know how passionate NBA fans are about this year's Rookie of the Year race, check in on the Utah Jazz and Philadelphia 76ers fans on Twitter. If you manage to make it out alive, you'll realize that as vehement as Sixers fans are that Simmons is this year's undisputed winner, Mitchell supporters across the globe are equally ardent and stubborn in the opposite view.

You'd be surprised how often the Rookie of the Year race is a complete runaway. While there has been only one unanimous MVP winner (Stephen Curry in 2016), there have been five unanimous Rookie of the Year selections -- including three in the last seven years. Basically, the Rookie of the Year is usually set in stone about 30 games into the season.

That's part of what makes this year so special.

Simmons, the No. 1 draft pick in 2016 who spent a year away from the court, had the award all but locked up midway through the season, but Mitchell, the No. 13 pick last June, came seemingly out of nowhere to become a legit contender. We won't find out who wins until June 25, but we already know that this is the most contentious Rookie of the Year race in NBA history. Here are a few reasons why:

1. The surprise factor

Not many knew what we would get from Simmons once he stepped on the court after missing his first year due to injury. We'd seen him play a handful of relatively meaningless games at LSU, but that was about it. Even during his first couple of summer league games, however, it was clear that Simmons would have an impact on the league -- we just didn't know he would be this good this quickly.

Mitchell arrived with much less fanfare out of Louisville, where he averaged a modest 15.6 points per game in his second and final season for the Cardinals. He was traded (by the Nuggets) on draft day, and started his season in and out of Utah's starting lineup. But by early November, it was clear that he was going to be driving the Jazz's offensive engine. When the Jazz got red-hot in the new year, Mitchell developed into a legitimate star.

While some rookies (LeBron James, Tim Duncan, even Andrew Wiggins) are known commodities coming out of college, part of the reason these two have been so compelling is that we really didn't know what we were in store for.

2. The moments

For Simmons, it came not too long ago. By April 6, he had been the Rookie of the Year frontrunner for five-plus months, but then he came out in the first quarter and absolutely destroyed LeBron James' Cavs in game that had significant playoff implications. Simmons was brilliant, throwing cross-court passes, showing off insane handles and throwing down monstrous dunks. All this without Joel Embiid, who some critics said Simmons couldn't consistently win without. The Sixers won the game, snatched the No. 3 seed, and Simmons had officially arrived.

For Mitchell it was against the Spurs in February. With the Jazz sitting at .500 in the midst of a 10-game winning streak, Mitchell erupted for 13 points in the fourth quarter to lead his team to a 101-99 win. He took over in the final minute, getting a steal and making a layup to give Utah the lead. Then, after the Spurs went back ahead by one, Mitchell hit a supremely confident pull-up dagger to put the Jazz ahead for good.

People already thought Mitchell one day could be the guy -- but now he was the guy. The Jazz went on to win 19 of their next 25 games.

3. The controversy

Is he or isn't he? Once Mitchell emerged as a Rookie of the Year candidate, it didn't take long for Simmons critics to say, "Yeah, but he isn't even a real rookie." Simmons sat out what would have been his rookie year last season after foot surgery, which led some to say that the advantages he gained in a full year as a professional athlete should disqualify him as a rookie. 

There's precedent -- Blake Griffin won Rookie of the Year after sitting out his first year due to a knee injury -- but that didn't stop everyone from having an opinion about it ... including Mitchell.

4. The beef

The pair went a long time without really acknowledging each other in any significant way. In fact, Mitchell consistently said that he didn't care about the Rookie of the Year award, and was solely focused on getting the Jazz to the playoffs. But that all changed earlier this week when Simmons said he was "100 percent" the Rookie of the Year, and then was publicly asked which rookies have caught his eye this year.

"None," Simmons said, via ESPN.

The normally humble Mitchell wasn't about to take that lying down, and he responded with the most savage pregame attire of the NBA season -- a black hoodie with the definition of the word "rookie" on the front -- implying that Simmons isn't a true rookie.

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Donovan Mitchell threw some shade Ben Simmons' way with his pregame attire. Utah Jazz Twitter

Game on, indeed.

6. The winning

Simmons and Mitchell were both exciting when we thought they were on fringe playoff contenders. The fact that two rookies are leading top-five seeds in each conference is unprecedented in the one-and-done era. Mitchell's Jazz had win streaks of 11 and nine games, while Simmons' Sixers ended the regular season on a 16-game winning streak, the longest ever heading into the NBA playoffs.

Players this young an inexperienced aren't supposed to win this much, and both Utah and Philly have vastly overachieved this season (based on preseason predictions), thanks in large part to their phenomenal rookies.

7. The saltiness

Sixers fans were flabbergasted that Joel Embiid (and Dario Saric) missed out on Rookie of the Year last season. Sure, he only played 31 games, but Embiid was far and away the best player in a relatively weak rookie class. It only added to the fans' ire that when Embiid was passed over, voters overwhelmingly voted for Bucks guard Malcolm Brogdon over their other rookie, Saric, who finished second. That recent perception of a snub has made Philly fans go on the offensive. Any time someone even suggests that Mitchell is close to catching or beating Simmons, the assault begins.

Meanwhile out in Utah the prevailing theory from fans is that national media constantly overlooks the Jazz and mines for any other story line to cover except for something possibly involving their team. The fact that Simmons plays in a much bigger market only adds fuel to their fire when it comes to the Rookie of the Year debate.

That's where these two passionate fan bases are coming from when they get antsy about the national media controlling this vote.

8. The history

Another part of what makes this race so exciting is the fact that we haven't had a good one in a long time -- we've been craving a rookie showdown like this. The most recent relatively close race was between Tyreke Evans and Stephen Curry back in 2010, with Evans taking home 67 first-place votes to Curry's 43 -- and neither's team sniffing the playoffs. LeBron James and Carmelo Anthony in 2004 seems like it could have been a great one, but LeBron beat Melo by 38 first-place votes. Elton Brand and Steve Francis tied in 2000, but that was 18 years ago, before some NBA fans were even born. The last close race between two future Hall of Famers was when Jason Kidd and Grant Hill tied in 1995.

Arguably the most memorable Rookie of the Year races of all-time (Michael Jordan vs. Hakeem Olajuwon and Magic Johnson vs. Larry Bird) happened in the early 1980s. All this to say, Simmons and Mitchell have brought the Rookie of the Year discussion back to the forefront, which has made people much more invested ... and angry.