The sweep is a width-creating pattern. Multiple attackers shift laterally across the field together to overload one side and create a numbers advantage on the outside.
The mechanics are a chain. The ball moves quickly through two or three attackers, with each receiver passing on as they receive. At the same time, the whole line of attackers is drifting toward the same side. By the time the ball reaches the outside, there are more attackers in that channel than there are defenders.
The sweep works because of numerical advantage. If three attackers move toward four defenders, no advantage. If four attackers move toward three defenders, the outside attacker is unmarked and can finish or pass to a free wing. The sweep is how a team manufactures that mismatch out of nothing.
It usually comes off a strike phase or a long carry that has already compressed defenders to one side. The sudden lateral shift attacks the under-defended side. It can also work as a standing-start strike call from a tap, a penalty restart, or a kickoff return.
The most common failure modes are forward passes (very common when players are moving laterally — the receiver has drifted ahead of the passer), the sweep being too slow so defenders slide across to match it, attackers bunching too close together and getting marked by one defender each, and forgetting to actually use the width — the ball has to reach the outside attacker for the play to mean anything.