Which rookie postseason star is the real ROY?

This year's NBA Rookie of the Year debate, one of the most fiercely contested in some time, has continued raging well after awards ballots were due two and a half weeks ago.

While most rookies either play small roles for contending teams or put up bigger per-game numbers on lottery-bound ones, Donovan Mitchell of the Utah Jazz and Ben Simmons of the Philadelphia 76ers have been driving forces in their teams' advancing to the second round of the playoffs.

As Mitchell and Simmons continue to shine on a bigger stage, let's revisit the question: Who has been this year's most valuable rookie?

Offensive value

The case for Mitchell as Rookie of the Year centered largely on his leading role in the Jazz's offense. Utah's 48 wins during the regular season were the most by a team led in scoring by a rookie since the 1989-90 San Antonio Spurs, who won 56 games behind rookie David Robinson (who was 24 at the time, having spent four years in college and two more serving in the Navy).

A focus on scoring does a disservice to Simmons' involvement in the 76ers' attack. While both Joel Embiid (22.9 ppg) andJJ Redick(17.1 ppg) scored more points than Simmons (15.8 ppg), Simmons ranked fifth in the league with 8.2 assists per game -- more than double Mitchell's 3.7 assist average.

Last season, I introduced the stat "combined usage" to quantify a player's role in the offense as both a scorer and a passer, adding the percentage of the team's plays that he finished with a shot, trip to the free throw line or turnover (traditional usage rate) to those on which he handed out an assist. While Mitchell still comes out slightly ahead, both players played historically large roles for rookies on winning teams.

Although Mitchell and Simmons operated in very different styles -- Mitchell creating primarily for himself, Simmons primarily for others -- their overall offensive value as rookies was similar. Basketball-Reference.com's box plus-minus metric (BPM) gives Mitchell the slight edge (plus-1.3 offensive BPM to Simmons' 1.0), as does ESPN's real plus-minus (plus-1.7 for Mitchell, plus-1.5 for Simmons).

Defensive value

Although Mitchell might deserve the nod as offensive Rookie of the Year, Simmons distinguishes himself at the defensive end of the court. Mitchell entered the league advertised as a strong defender -- that was probably considered his better skill as a prospect -- and lived up to expectations as part of the NBA's second-best defense during the regular season.

Nonetheless, Simmons was the more valuable defender. Part of that is simply about size and positional value. The 6-foot-3 Mitchell naturally matched up almost exclusively against perimeter players, whereas the 6-foot-10 Simmons was one of the league's most versatile defenders. He defended both guard spots and both forward spots at least 20 percent of the time and none more than 30 percent, per Second Spectrum matchup data, which tracks a player's defensive assignment for the majority of a given play.

Then there were Simmons' box-score contributions on defense. He rebounded nearly 20 percent of opponents' missed shots, making him above average for a power forward. Simmons was one of 16 regular players (minimum 1,000 minutes) in the league to average at least two steals per 100 team plays on defense and block at least 2 percent of opponent 2-point attempts.

As compared to forwards, Simmons' defense was more good than great. But if considered a point guard -- his offensive position, which allowed Brett Brown to play a big starting lineup with forwards Robert Covington and Dario Saric on the court as well -- he was elite. Simmons' plus-1.7 defensive RPM was ninth among guards and well ahead of Mitchell's plus-0.7 rating on defense. (Simmons had an even bigger advantage in defensive BPM because of an interaction term that values players who have high rates of defensive rebounds and assists, while Mitchell's defensive impact was probably underrated by box-score stats.)

Overall value

In an era when few rookies are immediately productive, Simmons, in particular, stood as an exception. His 10.1 wins above replacement player (WARP) by my metric ranked fourth among all rookies in the one-and-done era.

By this metric, Mitchell -- 24th in the one-and-done era with 5.2 WARP -- was less exceptional. But switching to RPM supports the notion that this was one of the strongest Rookie of the Year battles in recent memory. Both Simmons and Mitchell rank among the top 10 rookies of the past 18 seasons by RPM wins above replacement (WAR), which dates to 2000-01 -- as does Jayson Tatum of the Boston Celtics, the likely third-place finisher in Rookie of the Year voting.

Given how effective they were during the regular season, it's all the more remarkable that Mitchell and Simmons have both been even better in the playoffs.

Playoff value

Just as it has become rare for rookies to contribute as much to winning teams as Mitchell and Simmons have, so too has it been out of the ordinary for them to be such big factors in the postseason. Back through 2000, this year's duo ranks among the top six rookies in WARP per game in a playoff run of at least six games.

Mitchell's playoff run has been compared to that ofDwyane Wade leading the Miami Heat to the second round in 2004, and that holds up in terms of advanced statistics. While Wade didn't shoulder as heavy an offensive load as Mitchell, who is finishing an incredible 32 percent of the Jazz's plays in the postseason, Wade handed out 6.9 assists per 100 team plays -- more than double Mitchell's playoff mark. As such, they were similarly valuable in the playoffs.

With Embiid sidelined the first two games, Simmons was Philadelphia's best player in a comfortable 4-1 series win over the Heat. Even after a seven-turnover performance in the 76ers' Game 1 loss to the Boston Celtics, Simmons is posting the most WARP per game by a rookie in an extended playoff run since Tim Duncan in 1998.

In three of the past four seasons, Mitchell would have been an easy choice for Rookie of the Year, and in 2015-16, his strong RPM would have given him a reasonable case over Towns' superior box score stats. It's to Mitchell's slight misfortune that he happens to be putting together a strong rookie campaign at the same time Simmons has posted one of the best in recent memory.

Fortunately, while only one can win Rookie of the Year, there's plenty of room for both Mitchell and Simmons to emerge as stars in this postseason and beyond.

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