Everything in basketball revolves around time. The whole point of the game is to see who can score more points within a certain interval. Understanding the clock rules is essential no matter what level of basketball you're playing, coaching or watching. The rules for timing vary for high school, college and professional basketball.
High school games consist of four quarters lasting eight minutes each. College basketball rules call for two 20-minute halves. NBA games are divided into 12-minute quarters. Overtime periods also vary by level. High school overtime, when needed, is four minutes. In college and the NBA, overtime periods last five minutes.
Starting and Stopping Clock
The clock starts when a player touches the ball after the official tosses it for the initial jump ball. After that, the clock only stops when the official blows his whistle to indicate a foul, violation or timeout. The official may also stop the clock for an unusual delay, such as the ball rolling off the floor and away from play, or for an injured player. The clock starts again when it's touched inbounds after a throw-in, or when a player touches the ball on a rebound after a missed free throw.
End of Game Rules
Some timing rules change toward the end of the game. The clock stops during the last minute of the second half plus overtime periods in college after a made basket, and starts again once a player touches the ball inbounds following the ensuing throw-in. In the NBA, this rule applies to the last two minutes of the fourth quarter and any overtime periods. There is no similar rule in high school basketball. A basket counts if it leaves the player's hand and time expires while the ball is still in the air, and the shot goes through the hoop.
Last Shot Rule
In high school and college basketball, if there are three-tenths of a second or less left on the clock, players may not catch and shoot the ball for a successful field goal. A player may only tap or deflect the ball into the basket for the shot to be counted.