Per-minute performance is one of the most consistent things in basketball. However, guessing how many minutes players will play from season to season is a much more daunting task. We do a quick breakdown about how minutes change season to season in the NBA.
The NBA season approaches and we'll venture again into prediction territory. As a reminder, we do not find predictions to be a good test for production metrics. The key reason is that while it is fairly easy to predict how good a player is, it is hard to know how much they will play, and at what position. Injuries, coaching, and other factors can cause large swings in how minutes in the NBA are dolled out. I decided to do a quick examination of NBA history to show how minutes change year to year.
The first group of players I looked at was those that returned. From year to year, the majority of minutes are handed out to veterans. However, how those minutes are handed out varies. I took the difference in minutes for every season they played and looked at how different that total was year to year.* Here's what we got.
Yes, the returning set of players gets the lion share of the minutes from the previous season. Except, these are allocated much differently. For over the last decade the difference in minutes from returning players has accounted for almost one-third of the total minutes played! Players that are entering their prime start to get more minutes. Aging players start going to the bench. Random coaches decide various role players deserve more or fewer minutes than they were getting. In the end, even for returning vets it's hard to pin down exact minutes.
We're not done yet either!
Every season the NBA holds a draft that brings in a crop of new players. Some teams find talent from other leagues. And sometimes players that were sidelined for entire seasons return. And this means every year there's an influx of new minutes. I broke down how that looked as well.
This is not as severe as our returning players. And in recent years this has dropped. However, almost 10% of the minutes in a given NBA season are by players that weren't on the court the prior year. This is important for a key reason. While there are factors about rookies that translate to NBA performance, the majority of what a rookie will look like in the NBA is unknown. Even for good NCAA models, only 40% of a player's variance can be explained by their college numbers. That means every season a tenth of the league is new minutes from players that are highly unpredictable (rookies and players returning from long term injuries)
We have one last group to examine.
Of course, if new players come in, and existing players get different minutes, that means some minutes are lost. Players leaving to retirement, permanent injury, or that can't find an NBA team that wants them drop out. Here's a look at how many minutes are lost season to season in the NBA.
This is not as severe as our previous swings. However, you can expect somewhere between five and ten percent of the NBA to "disappear" season to season.
Between our three swings -- 30%+ minute changes, ~10% to new players, and 5-10% lost -- in any given NBA season almost half of the minutes are different than the previous season. Yes, per-minute production is important for determining success. But the minute part of that equation should make it clear that knowing who will be on the court is also important. One need only look at the Miami Heat with a healthy Dwyane Wade playing a full season versus an injured Dwyane Wade playing limited minutes to know that. Many analysts will guess how the upcoming NBA season will look. Most of them will know who the good players and bad players are. However, none of us will have a clear picture of how the minute landscape in the NBA will shake up. That is, of course, if history repeats itself.
*The season differences are normalized. That means the minutes were adjusted so the minutes in both seasons were the same and then a difference was taken using the current year's minutes. This was to help for things like the lockout seasons and changes in the NBA schedule length.