Goaltending and basket interference, explained
Why you cannot swat a ball on its way down, what the imaginary cylinder is, and how the two violations differ — for both defenders and attackers.
The core idea
Once a shot is on its way down toward the basket and has a chance to go in, defenders cannot touch it — that is goaltending. The rule stops tall players from simply blocking every shot at the rim, and it keeps a good attempt as a fair chance to score. A goaltending call gives the shooting team the points as if the shot had gone in.
Goaltending in detail
A block is goaltending if the ball is touched while it is above the rim and on its downward flight, or after it has hit the backboard on a shot attempt. The judgement is about the ball’s path: swat it on the way up and it is a clean block; touch it on the way down, over the rim, and it is goaltending.
The cylinder and basket interference
Above the rim there is an imaginary cylinder rising from the hoop. Touching the ball while it is on the rim or within that cylinder — from either team — is basket interference. Reaching through the net from below, or touching the rim while the ball is on it, counts too. It applies to attackers as well: tip a ball in while it sits on the rim and it is waved off.
Attacker vs defender
The consequences depend on who does it. Defensive goaltending or basket interference awards the basket to the offence. Offensive basket interference — an attacker touching the ball in the cylinder or guiding it in off the rim — is a violation that cancels the basket and gives the ball to the defence. Same principle, opposite outcome.