The jump circle in basketball is an area on the court where jump balls are performed. Jump balls are used to put the ball into play at the start of the game. They also decide which team gets possession when two opposing players are jockeying for the ball.
Before the game begins, it must be decided which team will start with possession of the ball. This is where the jump ball comes into play, with the referee throwing the ball directly into the air and allowing two opposing players to compete for it. The player that manages to tap the ball backwards to a nearby teammate has officially secured possession for their team. Jump balls are also used to start an overtime period if two teams are tied after four full quarters of action.
When two opposing players are both grabbing the ball and neither can pull away with it, the referee will call a 'held ball.' Once the determination is made, play temporarily stops as the two players make their way towards a designated spot on the court for a jump ball to decide which team ultimately controls the ball. When trying to resolve a held ball situation, jump balls do not take place at the center jump circle, but rather within the circle just above the painted area of the court.
The jump circle takes on a round shape for several reasons, the first being that it ensures the fairness of a jump ball. Each player stands on an opposite half of the circle, preventing one player from accessing the ball more easily than the other once its in mid-air.
The jump circle also gives the players that are not competing in the jump ball a reference point for where to stand. Each leaper's teammates assemble around the outside of the circle, standing far away enough so that they do not interfere with the contest, yet close enough to where they can grab the ball once it is tipped.