The clocks are the rules
Basketball's rulebook is long, but almost everything a new viewer needs sits in the clocks. The game clock counts down the quarter. The shot clock forces the attacking team to put the ball on the rim within a fixed window, and if it does not, possession changes hands with nothing to show for it. That single rule is the reason basketball has hundreds of possessions in a night while other sports have dozens.
There are smaller clocks layered on top. A team has a limited time to inbound the ball, and a limited time to carry it across the halfway line once it has. The effect is that a defence can attack the clock rather than the ball: press hard for six seconds, and the attack has already lost a third of its possession before the first pass into the front court.
When play stops and restarts, the shot clock sometimes resets fully and sometimes only partially — most commonly after an offensive rebound, where the attacking team keeps the ball but gets a shorter window. That partial reset is why an offensive rebound often produces a rushed second shot rather than a patient rebuild of the attack.
Fouls, the bonus and free throws
A foul is illegal contact. The immediate punishment is that the other team gets the ball, or free throws if the foul happened during a shot. The second punishment is slower and more important: team fouls accumulate through the quarter, and once a team passes the limit, every further foul sends the opponent to the free-throw line whether they were shooting or not. That is the bonus, and it changes how a defence can play in the last four minutes of a quarter.
Free throws are the only uncontested shot in the sport, which makes them strategically odd. Trailing teams deliberately foul to stop the clock and force them, accepting near-certain points in exchange for getting the ball back. It works only against poor free-throw shooters and only when the deficit is small enough for the arithmetic to close.
Personal foul totals matter individually too. Reach the individual limit and the player is out of the game entirely, so a star with early fouls often sits, not because the coach wants to rest them but because the alternative is losing them in the fourth quarter.
Violations that shape the floor
Travelling and double dribble police what a player may do with the ball. Three seconds in the paint polices where they may stand: no attacker may camp in the area under the basket, and the defensive version limits how long a defender can lurk there without guarding anyone. Both exist to keep the middle of the floor from silting up with tall bodies.
Goaltending and basket interference cover the moment the ball reaches the rim. Once a shot is on its downward path toward the hoop, it is untouchable. Without that rule, height alone would settle every game, and the block would replace the contest.
Backcourt violations stop a team from retreating once it has advanced, which forces attacks forward and denies the ball-keeping tactics common in other sports. Taken together, the violations are all versions of the same instruction: keep going forward, keep the middle open, and do not stall.