When an attacker misses a Shooting or Throwing roll, it may sometimes be important to see if any other targets in the line of fire were hit. The GM should only use this rule when it's dramatically appropriate–not for every missed shot in a hail of gunfire.

Each miss that comes up a 1 on the Shooting die indicates a random adjacent character was hit. If the attacker was firing on full-auto or with a shotgun, a roll of 1 or 2 hits the bystander. Roll damage normally.

Horses and other animals are possible targets when firing on mounted characters as well.

It's sometimes easier to hit an adjacent victim than the original target using this quick system. That may not be entirely realistic, but it's fast and simple, it makes large groups of people vulnerable to missile fire, and best of all, increases the drama of firing at opponents locked in melee with the attacker's allies.

Savage Worlds Deluxe Edition p. 83