Why the three-point line sits where it does

What the line was introduced to do

Before the arc existed, the most efficient shot was always the one closest to the basket, which concentrated play into a very small area. That concentration made the game physically congested and reduced the competitive value of accurate shooting from any distance. Awarding an extra point for a longer shot creates a reason to attack from outside, which pulls defenders away from the basket itself.

The intended effect was therefore spatial rather than statistical, opening the court rather than simply increasing the number of points scored. Scoring rose as a consequence, but the deeper change was in where players stand and how a defence has to be organised.

The arithmetic that followed

A shot worth an extra point only has to be made at a lower rate in order to be equally valuable, which is straightforward arithmetic. That relationship makes a moderately accurate long shot more valuable than an equally accurate shot from the middle distance. The mid-range shot is consequently squeezed, since it carries much of the difficulty of a long shot while offering none of the reward.

Teams reorganised around this once the arithmetic became widely understood, and the distribution of shot locations changed very sharply indeed. The rule did not change but the understanding of it did, which is a common pattern in any sport containing a scoring asymmetry.

Where the line is drawn and why it varies

The arc is not a simple semicircle, since it is cut off near the sidelines in order to keep the corner shot inside the playing area. That produces a noticeably shorter distance in the corners, which makes the corner shot the most efficient one available on the floor. Competitions place the arc at different distances, and a small change in the radius has a large effect on shooting percentages across a season.

Moving the line further out reduces the number of players able to shoot from it, which concentrates the skill rather than spreading it around. Any adjustment therefore trades spacing against accessibility, and current positions are settled compromises rather than optimal points.

What the line did to defence

Defences have to cover a far larger area than they once did, which raises the value of lateral speed and of constant communication. Help defence became more costly, since leaving a shooter in order to assist near the basket now surrenders a more valuable shot. Switching between assignments became more common because it avoids the long rotations that leave a shooter unattended in a corner.

The size and mobility of the players selected has shifted accordingly, favouring those able to defend across several positions. These changes were driven by geometry rather than by fashion, which is exactly why they have proved so durable.

The arguments about going further

Proposals to move the line back, or to add a further scoring zone beyond it, recur whenever long shooting appears to dominate. The case for change is that no single shot type should be so much more efficient than every available alternative. The case against is that the current balance produces open and fast basketball, and that the congestion it replaced was distinctly worse.

Any change would also break comparability with earlier seasons, which administrators tend to weigh more heavily than spectators do. The debate is really about how much of the court should be worth attacking, which is the same question the original line answered.