The short side attack is a pattern that exploits a defense that has overcommitted to the wide side of the field. When defenders shift their weight to cover the bigger space, the narrower short side becomes available — and there are usually fewer defenders there to deal with.
The setup builds across the previous touches. The attack moves the ball toward the wide side over two or three touches. The defense reads "they're going wide" and starts sliding that way. By the third or fourth touch, the defenders have rotated their feet, their eyes, and their positioning toward the wide side — and the short side has been vacated.
The strike is a reversal. The next attacker takes the ball back the other way, toward the short side. There is less open space there to run into, but there are also fewer defenders to beat. Often it becomes a clean 1-on-1 with the wing, or a corner finish, or an inside ball back to a supporting middle.
The short side is not about hunting for big open space — it is about hunting for a numbers advantage in a tight area. Two attackers against one defender in five meters is still an advantage.
The most common failure modes are attacking short before the defense has actually shifted (no real advantage), the pass to the short-side runner being slow enough that defenders rotate back, the attacker getting trapped in the corner with no support, and going short out of habit on every set rather than waiting for the defense to commit.