Note: This cannot be done with more than two weapons. Get a melee weapon (baseball bat, dildo, or a police nightstick) and an ordinary shotgun. If you have more than those two weapons this trick cannot be done. Switch to your melee weapon. Walk up to a pedestrian and hit them, then immediately press Circle to switch to your shotgun. If done correctly, CJ should hit the pedestrian with the shotgun as if he were using it as a melee weapon.
Back to Grand Theft Auto: San Andreas