A Chucker in basketball is a player who takes many ill-advised shots without making a high percentage of them. The term refers to someone who seems to just throw or chuck the ball at the basket without much thought or skill.
Chuckers often have a shoot-first mentality and rarely pass to teammates, even when they are open. They rely on taking a high volume of shots, usually from long range, in hopes of getting lucky and making some baskets.
However, their poor shot selection and low shooting percentage hurt their team's offense. While the term was popularized by the TV show Seinfeld, NBA players like J.R. Smith have been considered Chuckers due to their tendency to take frequent, low-percentage shots.