Bull Rush
You can make a bull rush as a standard action or as a charge attack. A bull rush attempts to push an opponent straight back without doing any harm.
If your attack is successful, your target is pushed back 5 feet. For every 5 by which your attack exceeds your opponent’s CMD you can push the target back an additional 5 feet. You can move with the target if you wish but you must have the available movement to do so. If your attack fails, your movement ends in front of the target.
An enemy being moved by a bull rush does not provoke an attack of opportunity because of the movement. You cannot bull rush a creature into a square that is occupied by a solid object or obstacle. If there is another creature in the way of your bull rush, compare your combat check to bull rush that creature with a -5 penalty for each creature beyond the first. If you are successful, you can continue to push the creatures a distance equal to the lesser result.