Posted by Neil Paine on June 3, 2010
Today I have a mailbag question from our friend David Biderman at The Wall Street Journal:
I had an NBA playoffs question. I took a quick (really quick) glance at the Celtics, and the first thing that jumps out is how balanced their starting five was during the regular season. Is there any way to quantify how balanced a team is? If so, could we do this for NBA finals teams?
Absolutely; in fact, it's a concept I looked into a bit for these posts:
However, I hadn't looked at NBA Finalists in particular yet, and I also would like to take this opportunity and try out a new metric to measure how balanced teams' starting lineups are.
The new metric (well, new to me at least) is called the Herfindahl-Hirschman Index (HHI), which measures how concentrated a market is among its firms. A monopolistic market will have a high HHI score, indicating that the majority of the market power rests with only a select few firms; conversely, a lower HHI score indicates a competitive market in which all firms have relatively equal shares. If you think of a basketball team as a market, you can apply this logic to a 5-man unit -- every player is working together to create points, but they're also "competing" against each other for touches and shots. A "monopolistic" lineup would be one where only one or two players take the majority of the possessions (think the 2000-02 Lakers with Shaq & Kobe), while a "competitive" lineup would be one where the offensive chances are distributed relatively evenly among the 5 players on the court.
So here's how I applied the HHI to Finals starting 5s... First, for every player in playoff history, I calculated Modified Shot Attempts (MSA):
MSA = 1.00 * (FG) * (1 - ((tmAST) / (tmFG)))+ 0.50 * (FG) * ((tmAST) / (tmFG))+ 1.00 * ((FGA) - (FG))+ 0.44 * (FTA)+ 0.50 * (AST)
This is essentially a measure of possessions used, except without turnovers because -- regrettably -- we don't have individual turnover stats for years before 1978. I then calculated the percentage of the team's MSA the player used when on the court (%MSA). For every Finals team ever, I isolated just their top 5 players in minutes -- not always necessarily their 5 starters, but usually the two groups are basically the same -- and scaled their %MSA to add up to 100% for that 5-man unit. I called the scaled %MSA term "share" -- as in market share, if the 5 man unit is a market and each player is a firm competing to use possessions. That way we can calculate the HHI, which is equal to the sum of the squared shares for a team. Here are the most imbalanced NBA Finals teams ever:
Wow, lots of MJ there. And at the other end of the spectrum, here are the most balanced Finalists ever:
It's truly remarkable how balanced the 1973 Knicks were -- consider that a "perfect" HHI for a basketball team would be 20% (5*0.2^2), which was almost exactly the Knicks' score that year (technically it was 20.0328%, but that's close enough). Their top player by "share" was Walt Frazier with 20.8%; their starter with the lowest share was Bill Bradley with 18.7%. That's amazing, because it means on any given Knick possession, any of their starters were basically just as likely to put pressure on the defense. With easily the league's best estimated Offensive Rating in the playoffs (102.1, 3 pts/100 poss. better than the #2 Celtics), it's easy to see why those Knicks were a nightmare to defend that postseason.
But in total, how does team balance affect the outcome of a Finals series? Here is every Finals matchup since 1952, and how their HHI scores compared:
In the 58 NBA Finals from 1952-2009, the more balanced team won just 43.1% of the time -- and that's bad news for Boston, whose 21.2% HHI is lower than L.A.'s 21.9% mark. In general, this backs up what I found here, which was that teams with a more imbalanced attack, concentrating most of their possessions among only 2 players, were more successful that those who evenly spread their possessions among more of their starters. But before you write off the Celtics, remember that this group bucked that trend once before: in the 2008 Finals, L.A. was a team constructed much more like a typical NBA champ than Boston, but the Celtics prevailed anyway. Over the next few weeks, we'll find out if they can beat the odds again, or if the Lakers' traditional championship construction wins out this time around.