From trapezoid to rectangle: how the paint changed shape
Court history
The lane used to flare outwards under international rules and now it does not, and the change altered where big men stand.
The painted area under each basket, usually called the paint, the key or the lane, is now a rectangle in essentially every senior competition. It was not always. Under international rules until 2010 it was a trapezoid, narrow at the free throw line and flaring out to a wide base along the baseline.
The shape mattered because of the three second rule. An attacking player may not stand in the painted area for three consecutive seconds unless the ball is in the air on a shot or he is actively leaving. A trapezoid with a wide base pushed post players further out toward the sideline when they wanted to set up close to the basket, because the legal standing spot was further from the rim on the baseline side.
Changing to a rectangle brought international courts into line with the professional shape and gave the post player a position closer to the basket on the block. It also standardised the distance for a whole category of skills, from the drop step to the hook shot, so that a player moving between competitions did not have to relearn his footwork.
There are markings along the sides of the lane that new viewers rarely notice. The short perpendicular lines mark the rebounding spaces used during a free throw. Players line up in those slots in a fixed order, defenders taking the two spots nearest the basket, and nobody may step into the lane until the ball leaves the shooter's hand. The shooter himself may not cross the free throw line until the ball hits the rim.
The free throw line itself sits 5.80 metres from the baseline, which puts the shooter 4.60 metres from the backboard, and the semicircle drawn on top of the line completes the older circular key shape. That semicircle has no function in the free throw itself. It is used for the jump ball and, in some rule sets, as a boundary for other situations, which is why it is still painted even though the key around it changed.
If you watch a post-up now, count silently to three while the big man has his back to the basket inside the paint. Either the ball arrives, or he steps a foot out and back in to reset the count, or the whistle goes. That small step out is one of the most repeated movements in the sport and almost nobody notices it.