Is Jaylen Brown still a ‘prospect’? Plus, NBA pick-six All-Stars and the best player without a retired jersey

How long can a young NBA player be considered a prospect?

Although that distinction could be a matter of semantics, it has a practical impact on how we evaluate players in their early-to-mid 20s for trades and free agency. In his discussion of the Boston Celtics potentially trading for Kevin Durant on the Lowe Post earlier this week, ESPN’s Zach Lowe highlighted the possibility of Jaylen Brown (who turns 26 in October) continuing to take steps forward in his development.

One of the factors the Celtics must consider as they ponder a possible Durant trade is whether Brown is close to a finished product or can be expected to grow from a one-time All-Star into a player in the mix for All-NBA spots. Let’s take a look at what history can reveal.

Throughout the NBA season, I answer your questions about the latest, most interesting topics in basketball. You can tweet me directly at @kpelton, tweet your questions using the hashtag #peltonmailbag or email them to peltonmailbag@gmail.com.

(I’m also answering mailbag questions on YouTube.)

In addition to the main question, this week’s mailbag also tackles “pick-six” steals in the NBA and the best NBA players never to have their jerseys retired.

“What is the prospect cut off? At what point is a player likely what he is?”

— Seth

This is an interesting question in part because of the different definitions currently in use. For symmetry, our annual top 25 under 25 rankings make age 25 the point when players cease being prospects, while the Dunc’d On Basketball NBA podcast sets the bar slightly lower at age 24.

Realistically, there’s no one point where players are what they are. It’s always possible for individual outliers — such as Kyle Lowry — to develop into All-Stars in their late 20s. However, there probably is an age at which these kinds of transformations become far more the exception than the expectation.

To study this, I sliced my wins above replacement player metric (WARP) data for players who entered the league since 2002 and have reached at least age 32.

First, I found the most total WARP for these players over any three-year span of their career, which measures peak value. Naturally, LeBron James (75 WARP) leads this group, followed by former MVPs Kevin Durant (64), James Harden (63.5) and Stephen Curry (63).

Then I looked at which measures of player performance through a given age best predicted those peaks. That turned out to be WARP the previous season and over the past three with an adjustment for age. Armed with those two statistics, I separated the group of players by age and ran separate linear regressions to see how well they predicted three-year peak by age.

The results look more or less like you might expect. When players are in their early 20s, there’s a lot of uncertainty about how good they’ll eventually be. Only slightly more than half the variation in peak value can be explained by performance to date. By the time players reach the point at which they typically top out, in their mid-to-late 20s, variation in recent performance explains more than 85% of peak value.

The important question is when the curve of explanatory power of the regression vs. age flattens out. That happens a bit later than I expected — not until seasons the player finished at age 26. Admittedly, that’s pretty late to describe a player as a prospect. I think 25 is probably a good cutoff for that because the added predictive power between 25 and 26 is less substantial than at earlier ages. We also see far fewer sizable jumps in projected peak value at age 26 than 25.

Still, to focus an individual like Jaylen Brown, jumps are still possible. Perhaps the best hopeful comparison for Brown in our sample is DeMar DeRozan, who had also been a one-time All-Star entering his age-26 season but had never made All-NBA. DeRozan averaged a career-high 23.5 PPG in 2015-16, and was voted All-NBA third team as the Toronto Raptors reached the Eastern Conference finals.

If Boston hangs on to Brown, that’s the kind of incremental advancement they’ll be hoping to see.

This is something Second Spectrum’s Insight tool allows us to quantify. Here were the leaders during the 2021-22 regular season in “pick-six” steals that led immediately to scores by the player who came up with the steal unassisted.

Mikal Bridges finished in the top 10 in this category and was the leader among the 11 players who received votes for Defensive Player of the Year last season (Matisse Thybulle of the Philadelphia 76ers was next among that group with 21 pick-sixes, while winner Marcus Smart had just nine).

Although the likelihood of turning into a fast-break score on the other end is one of the reasons I think steals are generally undervalued, I’m not sure this should be a big consideration in Defensive Player of the Year voting. After all, rim protection is still the defensive skill that translates most consistently into strong team defense, and there’s nothing magical about pick-sixes as compared to steals that lead to teammates scoring in transition.

It is interesting to note that Smart’s steals yielded the worst offensive rating on the subsequent possession (1.2 points per possession) among the 14 players with at least 100 steals in the regular season, per my analysis of play-by-play data. But Thybulle (1.5 points per possession) was atop this group ahead of his former college teammate Dejounte Murray despite being outside the top 10 in pick-sixes.

Although Jack posed this question back in March, it remains relevant as Kyrie Irving‘s future with the Brooklyn Nets looks murky. I do think Irving will ultimately have his jersey retired by the Cleveland Cavaliers after hitting the biggest shot in franchise history to clinch the team’s only NBA title, but suffice to say the Boston Celtics won’t be retiring Irving’s number and things aren’t looking good in Brooklyn.

As for the second part of the question, the answer — with an asterisk — is George Mikan, the NBA’s first great player. Because the Lakers subsequently moved from Minneapolis to Los Angeles, Mikan’s No. 99 is officially “honored” by the Lakers but not considered retired.

There’s a similar explanation for why Hall of Famer Gary Payton hasn’t had his jersey retired. Payton was just a year into retirement when the Seattle SuperSonics moved to Oklahoma City and has rejected the idea of a ceremony in a city where he never played. Instead, Payton is waiting for the Sonics to return. Paul Arizin retired before the Warriors moved from Philadelphia to the Bay in 1962 and has never had his jersey retired as a result.

Hall of Famer Artis Gilmore is also in an interesting spot because his best years came with the now-defunct Kentucky Colonels of the ABA. Had Gilmore spent his NBA prime with another franchise, his jersey might be retired, but the Chicago Bulls have understandably been picky, retiring just four numbers in franchise history (Michael Jordan, Bob Love, Scottie Pippen and Jerry Sloan).

I was most surprised to discover that Steve Nash’s jersey wasn’t retired by the Phoenix Suns, for whom he won two MVPs. The Suns did induct Nash into their ring of honor and give him a similar ceremony, so I’m not sure whether he actually counts toward this question.

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