Jump ball and the possession arrow, explained
How a game starts, what happens when two players tie up the ball, and why some leagues use a jump ball while others use an alternating arrow.
The opening tip
Every basketball game begins with a jump ball at centre court: the referee tosses the ball straight up between one player from each team, and they try to tip it to a teammate. That opening tip decides who gets the ball first — and, in some leagues, sets up the rule that governs the rest of the game.
Held balls
A "held ball" (or tie-up) happens when two opponents both get firm hands on the ball at the same time, so neither can win it cleanly. Rather than wrestle, play stops and possession is decided. How it is decided is the big difference between the rulebooks.
Jump ball vs the arrow
The NBA settles held balls the old-fashioned way: another jump ball between the two players involved. FIBA and college basketball instead use the alternating-possession arrow — after the opening tip, held balls (and many other situations) simply go to whichever team the arrow is pointing to, and then the arrow flips. It keeps the game moving and removes the height advantage of a repeated jump.
Why the arrow exists
The alternating arrow was introduced to make possession fairer and faster. Repeated jump balls favoured the team with the best leaper, and stopping the game for a fresh toss every time slowed things down. The arrow shares those 50-50 situations out evenly and predictably — which is why most of the world outside the NBA uses it.