You can make a bull rush as a standard action or as part of a charge, in place of the melee attack. You can only bull rush an opponent who is no more than one size category larger than you.
A bull rush attempts to push an opponent straight back without doing any harm.
If you do not have the Improved Bull Rush feat, or a similar ability, initiating a bull rush provokes an attack of opportunity from the target of your maneuver.
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 unless you possess the Greater Bull Rush feat.
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, you must immediately make a combat maneuver check to bull rush that creature. You take a –4 penalty on this check for each creature being pushed beyond the first. If you are successful, you can continue to push the creatures a distance equal to the lesser result.
For example, if a fighter bull rushes a goblin for a total of 15 feet, but there is another goblin 5 feet behind the first, he must make another combat maneuver check against the second goblin after having pushed the first 5 feet.
If his check reveals that he can push the second goblin a total of 20 feet, he can continue to push both goblins another 10 feet (since the first goblin will have moved a total of 15 feet).