It can be surprising how many bullets are fired in a gunfight with no real intent of actually hitting the opposition. Often one fires simply to keep the enemy's head down in order to allow others to move safely.
At the end of a round, suppression is calculated against any individual who was fired on. This includes characters against whom dice were rolled as part of a clustered attack. Add up every attack die rolled against the target from shooting attacks, regardless if they did damage or even hit. This includes attack dice from explosive weapons. If the total is higher than the character's Stature, then the character is Suppressed.
A Suppressed character must make Full Defence action on their round, and takes a Stress point.
Example
Roxy Blitz takes cover behind a concrete highway divider as a triplet of Golden City agents empty their autopistols at her, all of them firing two shots each. None of them manage to hit, but as Roxy only has a Stature of 1, she spends the turn trying to make herself as small as possible and praying to Washington that their aim doesn't get better.