Before the alternating possession rule began in 1981, jump balls were common throughout games.
A shot bounces off the rim and away from the basket. Players from opposing teams grab the ball and fight for possession. The referee blows his whistle and calls a jump ball. What happens next depends on which level of basketball you are watching. In the National Basketball Association, the two players would undergo a jump ball tossed by a referee. But at nearly every other level, the alternating possession rule determines which team gets the ball.
The Rule's Origin
Before 1981, from instructional leagues through the professional level, when two players from opposing teams held control of the ball at the same time, a referee would call a jump ball. The two players would then line up facing each other in the circle nearest the violation. Their teammates would spread out around the circle. A referee would toss the ball in the air between them, and the two players would jump up and try to tip the ball to a teammate.
But college basketball introduced the alternating possession rule in 1981, and most other playing levels except for the NBA soon followed.
With the alternating possession rule, instead of a tip-off as described previously, one team is awarded the ball based on a possession arrow maintained at the scorer's table. Games still begin with an opening tip-off at half-court. But after the opening tip, the possession arrow is set to point toward the team that loses the tip-off. If a jump ball is later called, that team is awarded possession of the ball and in-bounds the ball. The possession arrow then switches to point toward the other team.
Confusion Over Out of Bounds
It happens rarely, but when a ball is knocked out of bounds and the referees can't determine which team touched the ball last, they can call a jump ball. In this case, the team to which the possession arrow is pointing receives the ball. The possession arrow then alternates to point to the other team.
Since jump balls are only executed at the start of each game and the start of an overtime period, how is possession determined for the outset of each half, or each quarter in the case of high school, middle school and lower-level competition? The ball is in-bounded by the team to which the possession arrow is pointing at the end of the previous half or quarter. Note that college games consist of two halves; games at other levels are comprised of four quarters. After the ball is in-bounded, the arrow changes to point to the other team.