By Robert Feinberg
The ancient Greek philosopher Heraclitus once said that change is the only constant in life. While his teaching is from thousands of years ago, it can easily be applied to the rules of modern day sports. Rules have been constantly tweaked and adjusted for decades across all sports. While the NBA has made many rule changes such as adjusting its defensive rules, banning and unbanning the slam dunk and implementing a shot clock, the introduction and altering of the 3-point line has had one of the most dramatic impacts on the association out of any rule change in league history.
The 3-point shot made its debut in the NBA in the 1979-80 season, and it was originally called a “gimmick” in the New York Times’s season preview. Phoenix Suns coach John Macleod said, “It may change our game at the end of the quarters, but I’m not going to set up plays for guys to bomb from 23 feet. I think that’s very boring basketball”. Boston Celtics’ president Red Auerbach stated that, “We don’t need it. I say leave our game alone”. In the first season of its existence, the shot was a rarely used weapon as teams averaged only 2.8 attempts per game. To put that into perspective, teams averaged 27 attempts per game in this 2016-17 season. Three-point shots per game gradually increased over the 1980s, as coaches finally realized that a shot that is worth 50% more pays off, even if that shot is a little harder to make. Ex-Nets coach Lawrence Frank said, “Teams have all caught on to the whole points-per-possession argument”. By 1994, teams were averaging nearly 10 attempts per game, then the NBA made one of its most impactful rule changes of all time. As a result of below average scoring in the early 1990s, the league moved the 3-point line closer, hoping the easier shot would result in higher scoring games. The line was originally 23 feet 9 inches (22 feet in the corners), and they shortened it by 21 inches to a uniform 22 feet at the beginning of the 1994-95 season. Although the average number of 3-point attempts per game increased by over 50%, the line was moved back to its original distance after the 1996-97 season because the shortened line had lowered the average score of games even further. In the three seasons before the line was moved in, teams averaged 105.6 points per game, while in the three seasons with the shorter line, teams averaged only 100.8 points per game. When the line reverted back to its original distance, there was a slight decrease in 3-point attempts the following season, however teams increased their attempts over time, soon surpassing the average amount of attempts that were taken when the line was moved in. Today, the 3-point shot is far from the “gimmick” it was considered to be in 1980. The shot plays a huge role in teams’ strategies, and players of all positions are expanding their range past the arc. Considering how significant the 3-point shot is in today’s league, it is important to investigate the effect the 1995-1997 experiment had on the NBA’s teams – Did the moving of the line help or hurt good 3-point shooting teams?
To test this, I used team per game stats from the 1992-93 season through the 1998-99 season and sorted the stats into the two seasons prior to the shortening of the 3-point line, the three seasons with the closer line, and the two seasons after the line was moved back out to its present distance. I created variables to represent the means of win percentage, 3-point percentage and 3-point makes per game for each team from the three different eras – e.g. “Average 3pt percentage before line moved in” is the average 3-point percentage for each team in the two years before the line was moved in. The summary statistics for the averages of teams’ 3-point percentages and 3-point makes per game is shown in Table 1 below
Table 1
Then I generated variables to represent the difference in teams’ average win percentages, average 3-point makes per game and average 3-point percentages between the different eras. Table 2 below shows the summary statistics for the latter two statistics.
Table 2
To test my hypothesis, I regressed difference in average win percentage when the line was moved in on average 3-point makes per game and average 3-point percentage in the era before the move. Then I regressed difference in average win percentage when the line was moved back out on average 3-point makes per game and average 3-point percentage while the line was moved in.
I found that how many 3-pointers a team was making per game before the line was moved in and how high their 3-point percentage was before the line was moved in had no statistically significant effect on their difference in win percentage once the line was moved in. However, when the line was moved back out to its present distance, 3-point makes per game during the period with the closer line and 3-point percentage during this period had a statistically significant effect on teams’ differences in win percentage when the line was moved back out.
First, we look at the regressions of difference in average win percentage when the line was moved in on average 3-point percentage and average 3-point makes per game in the two years before the move.
Table 3
As shown above, neither 3-point makes per game before the move nor 3-point percentage before the move had a statistically significant effect on a teams’ difference in win percentage between the era with the closer line and the era before it was moved.
Next, we look at the regressions of difference in average win percentage after the line was moved back out on average 3-point percentage and average 3-point makes per game during the era with the closer line.
Table 4
As shown in table 4 above, both 3-point makes per game during the three seasons with the closer line and 3-point percentage during these seasons had a statistically significant effect on a teams’ difference in win percentage between the era with the line moved back out and the era with the line moved in.
When interpreting the results of this study, it is important to look back at the summary statistics of the differences in average 3-point makes per game and average 3-point percentage between the different eras (Table 2, which is shown again below).
Table 2
First, the moving in of the 3-point line had no effect on teams’ differences in average win percentages because every team began making more 3-pointers and shooting them at a higher percentage when the line was moved in. The increase in percentage is what I would expect, assuming a closer shot is easier to make than a further shot, thus the increase in makes would also be expected under the assumption that teams were more willing to shoot the easier 3-point shot. As shown in table 2, the minimum increase in average 3-point makes per game was nearly one make per game, and the maximum increase was just over four makes per game.  Since the improvement in these two statistics were consistent league-wide, no teams gained a comparative advantage.
However, the effects of moving the 3-point line back out is a different story. While some would expect that the effects of moving the line back to its original distance would result in the exact opposite of what happened when the line was moved in, this was not the case. Even though the 3-point shot was made more difficult when it was pushed back 21 inches, not every team began making less 3-pointers or shooting them at a lower percentage. Table 2 shows that while the league average 3-point makes per game and 3-point percentage decreased, it was not the case for every team, as the maximum observations for both those variables were positive numbers. While making the 3-point shot easier helped the shooting of every team, making the 3-point shot more difficult did not hurt the shooting of every team. Because the moving back of the line affected teams differently, there was room for a comparative advantage.
According to the regressions, teams that were making a lot of 3-pointers when the line was moved in and shooting them at a high percentage had the largest drop in win percentage when the line was moved back out. One way to interpret this is that teams that had been getting a larger portion of their scoring from threes now had to either get their scoring from a more difficult 3-point shot or change their offensive game plan to include a higher proportion of 2-pointers. Therefore, the teams that weren’t making many threes (or were shooting them at a low percentage) while the line was moved in closer received a comparative advantage when it was moved back out because they didn’t have to change their offensive game plan as much as the teams that were relying heavily on the closer 3-point shot.
In an era where there is debate on if it is time to move the 3-point line back even further because of how proficient players have become at the shot, this post provides valuable information on how the moving of the line in the past has affected the NBA’s teams.
Editor’s Note: This article is a condensed version of a research paper conducted for the Harvard Sophomore Economics Tutorial Econ 970: Sports Economics. If you would like to read the full-length paper, please contact Robert at robertfeinberg@college.harvard.edu.
