Crouch Spam
Spamming crouch to move your head height up and down and throw off aim that is hunting for headshots.
Against headshot heroes like Widowmaker and Cassidy, you change your head height — the line their shot is predicted on — irregularly. Where jump shooting disrupts tracking with a large vertical movement, crouch spam is a separate mechanic that jitters the hitbox by shifting head height in small increments, and the community generally holds it to be more effective than jump shooting against higher ranks (because a jump trajectory is easy to read). It is useful not only mid-duel but also at a wall edge combined with jiggle peek. On the other hand, your movement speed drops while crouching, so in a retreat where you have no intention of shooting back it risks taking more damage. It reduces head damage not only against snipers but also against close-range, high-damage heroes.
When dueling opponents with high headshot value like Widowmaker, Hanzo, or Cassidy, spam crouch to jitter your head height while landing return fire. Combine it with jiggle peek: crouch in the instant you expose your body at a wall edge to break their head-line prediction.
Spamming crouch while retreating, getting run down because of the movement speed loss, and taking more damage as a result. Or letting the crouch rhythm become regular, so a flick player reads your head height and lands shots in a cluster.