Rugby sevens uses the same basic scoring system as union, but the clock creates a different sport. A short match means one restart, one card, or one missed touch-finder can decide the whole game.
A normal sevens match is much shorter than a 15-a-side union match. The usual shape is two short halves with a short interval, which lets tournaments run many matches across one or two days.
Like rugby union, play does not always stop the instant the clock reaches zero. If the ball remains live, the referee can let the phase finish until the laws provide a natural stoppage.
That is why the team in possession may keep the ball alive after the hooter. A penalty, free-kick, scrum, lineout, knock-on, touch, or dead-ball outcome can decide whether there is one more play or the half is over.
When a sevens match must produce a winner and the score is level, competition rules provide extra-time procedures. These periods are short, and sudden-death or first-score formats are common in major tournaments.
One major rhythm difference from 15s is the restart after a score. In sevens, the team that scored kicks off. That gives the scoring team a chance to regain possession immediately and turns restart execution into a core attacking skill.
A poor restart can hand the opposition the ball and field position. A strong contestable restart can turn one try into two before the other team has properly reset.