You can bash with a shield instead of using it for defense.
Shield Bash Attacks
You can bash an opponent with a shield, using it as an off-hand weapon. Used this way, a shield is a martial bludgeoning weapon.
For the purpose of penalties on attack rolls, treat a heavy shield as a one-handed weapon and treat a light shield as a light weapon.
Weapon Feature(s): shield
Pathfinder RPG Core Rulebook. Copyright 2009, Paizo Publishing, LLC; Author: Jason Bulmahn, based on material by Jonathan Tweet, Monte Cook, and Skip Williams.