The Celtics have come a long way in a short time. With their win in Madison Square Garden, the Fightin’ Brad Stevenses reached the 50-win mark with five games still to play. It was only three seasons ago that they were languishing near the bottom of the league with 25 wins. When fans think about a team “rebuilding” I guess this is what they imagine. A quick turn at the bottom of the league, a high draft pick, a few smart trades and signings, and a steady track of progress back up the standings.

In reality, it’s rarely so simple. What Boston has managed since breaking up their title core isn’t unprecedented but it is rare. Since the NBA/ABA merger in 1976, there have been 222 seasons where a team won fewer than 30 games (for shortened seasons I’ll use Win%*82 games). Let’s look at how many teams experienced a rebuild that looks something like Boston’s.

Bad Season Clustering

The first notable characteristic about Boston’s bad 2014 season is that it stood alone. The franchise hadn’t had a sub-30 win season since 2007 and are now three years away and don’t seem likely to fall back below 30 anytime soon. It’s not surprising that bad teams usually have more than one rough season at a time, but it might be surprising just how clustered bad seasons are. Over 80% of sub-30 seasons either immediately follow or proceed another sub-30 season. Another 8% are two seasons ahead or behind a franchises’s nearest other sub-30 year and 5% more are within three seasons. Only 10 post-merger sub-30 win seasons have been more than 5 years away from another sub-30 season for the same franchise.

If Boston stays over 30 wins for the next three seasons, which seems a good bet, they’ll join that exclusive club. Amazingly, three of those ten seasons are already owned by the Celtics’ franchise as all their other sub-30 seasons in this era (1979, 1997, 2007) were similarly isolated from other truly bad years.

Franchise Year Wins Prior Sub-30 Next Sub-30 Years Gap Celtics 1979 29 1950 1997 18 Suns 1988 28 1969 2004 16 Celtics 1997 15 1979 2007 10 Spurs 1997 20 1989 8 Rockets 2002 28 1984 16-18 Magic 2004 21 1992 2013 9 Suns 2004 29 1988 2013 9 Jazz 2005 26 1982 2014 9 Pelicans 2005 18 2012 7 Celtics 2007 24 1997 2014 7

Distance to 50 Wins

If the first notable characteristic of Boston’s rebuild is how briefly they stayed bad, the second is how quickly they became good. The Celtics only spent two years in the broad middle of the league between the 30-49 wins where teams are neither terrible or contenders.

To measure the rarity of this, we can cut out twelve recent seasons where the team hasn’t reached a 50-win season yet and check how long it took to get to 50 from the other 210 sub-30 seasons. Amazingly, seven franchises have gone sub-30 to 50+ in one season. Boston, San Antonio, and Phoenix have each done it twice with the Nets owning the remaining occurrence. Another eight teams have managed it in two years and then a group of 19 have done it, like the Celtics, in three years. That means that only 16% of post-merger sub-30 win seasons have been followed by a 50-win season as quickly as Boston’s. If the C’s make it to 52 wins, which they likely will, that drops to only 12%.

There are 33 sub-30 win seasons that are now 3-9 years in the past and have not yet been followed by a 50-win year. If we remove those, we’re left with 177 seasons. From those, over 40% took ten or more years to get from <30 to >=50 wins. The Celtics’ stay at the bottom and rise to the top have both been short in historical context.

Steady Growth

The final major characteristic of Boston’s rebuild is the continual growth. Improvement in the NBA isn’t always linear (or logarithmic if you want to get particular) as even teams that improve over the course of a few seasons often mix in a year of stagnation or decline. For example, the Bucks won 15 in the year the Celtics won 25 and should climb up into the mid-40’s this season, but went 15 ↑ 41 ↓ 33 ↑ 40+ along the way.

If we loosely define “improvement” as adding four wins over the previous season, we can see how rare Boston’s consistent growth would be if they can just reach 52 wins this year. As you would expect for teams starting bad, 131 of the 211 sub-30 seasons (where we have enough history) were followed by a year of at least four additional wins. Of those 131, only 60 managed the same level of improvement in year two. Of the 60 survivors, only 21 continued on for a third season; three of those managed the three season growth but didn’t even get over 40 wins in the process.

We’re left with only 10% of sub-30 win seasons being followed by just three years of modest wins improvement. The Celtics haven’t reached that mark yet but only need to go 2-3 to close the season to achieve it. If they were to close 4-1 they could be only the sixth team in 40 years to add 6+ wins for three straight seasons after a sub-30 win year.

Complete Context

We now know that each of the three main characteristics of the Celtics’ rebuild are relatively rare on their own. Less than 5% of sub-30 win seasons are as isolated from similarly bad years. Only 16% of sub-30 win seasons are turned into 50+ win years in three or less years. Only 10% of sub-30 win seasons are followed by three or more consecutive seasons of growth. If Boston can win two more games this season they’ll accomplish all three of those things at once.

Only one franchise has managed that in the post-merger NBA, but they don’t look much like this Celtics team. The 2007-08 Miami Heat had an injury riddled 15-win campaign. They blew their draft pick by taking Michael Beasley but jumped all the way to 43 wins just by getting healthy. They climbed to 47 the following year, then changed almost their entire roster in signing LeBron James and Chris Bosh before season three. That’s the only comparable looking build by the numbers, though the current Jazz look a lot more similar in reality.

We’re left with a series of seasons that both follows the archetype of what fans think of as a rebuild, and yet is nearly unprecedented in NBA history. It looks remarkably rare for a franchise to quickly hit bottom then quickly but steadily climb back to near the top of the league in only three years. To have done that with minimal on-court value provided by the major parts of the Nets trade is even more exceptional. In October of 2013 this was a capped out team filled with middling, past-it, and injured veterans. Three years later they sit atop the Eastern Conference, and in the process have somehow added significant draft capital to where they were back then. This, it seems, should not be possible.

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