This season's rookie class has been phenomenal, but the Rookie of the Year is likely to be Ben Simmons -- who of course was actually picked in the 2017 NBA Draft. Simmons didn't play last season because of a foot injury, so he's still a rookie this season by the NBA's rules, but there's been a running argument that he's not a true rookie because he had all last season to become accustomed to the NBA lifestyle. 

In particular, Utah Jazz fans have taken up that argument in support of their star rookie guard, Donovan Mitchell. Even Mitchell himself has bought in, wearing different sweatshirts alluding to the technicality of what rookie actually means. It's a little goofy, sure, but stuff like this is what makes the NBA so interesting to follow. 

During Game 1 of second-round series between the Celtics and 76ers, Mitchell found an ally in the Boston crowd. The TD Garden faithful taunted Simmons with "not a rookie" chants throughout the game. Mitchell, understandably, found it hilarious. 

Later in the game, Celtics fans switched things up a little bit, chanting "he's a rookie" in support of their own star rookie, Jayson Tatum

The No. 3 overall pick finished with a playoff career-high 28 points in the Celtics' 117-101 win in Game 1.