The Grandfather wrote:
The action you describe can only be done as a full-round action (i.e. no move action can be made in conjunction with it)...
Right. The only movement that can be made during a full round action is a 5 foot step.
PPHB: "The only movement you can take during a full-round action is a 5-foot step before, during, or after the action. You can also perform free actions and swift actions..."
The Grandfather wrote:
Keep in mind that your free bull rush attacks might make you unable to reach your enemies with your melee reach.
The Shield Bash/Shield Slam attack would be used as a tool in the utility belt of a sword and board fighter. Here is an example of the shield bash in action!
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Sylvianna the thief/mage and Tartann the fighter finish off the last of the kobold zombies in a tough battle. Sylvianna has sustained a great deal of damage and takes a moment to bind her wounds.
After casting detect magic from a scroll, she is drawn to a cleverly hidden chest in a corner of the room housing items that radiate a strong alteration magic. Carefully looking it over she finds a powerful acid trap guarding from anyone foolish enough to open it.
Sylvianna bends down and starts to disable the tricky trap on the ornate chest. She is carefully working past the sensitive triggers that would spray acid all over anything in a 10 foot radius.
Tartann is looking nervously from her to the chest hoping she doesn't kill them both. He hears something from the hall and turns to look.
Just then Ruggle the goblin dressed in blood stained studded leather enters the room. He is supprised to see his kobold slaves scattered dead around the room and an elf and dwarf standing in the corner. There is rage on his face as he points to Sylvianna. He rushes toward Sylvianna and says in barely intelligible common, "Keep your hands off my stones (pun intended)."
In his rage Ruggle makes a mistake and tries to run past Tartann in an effort to stop Sylvianna from opening the chest. Doing this provokes and attack of opportunity (AO) so Tartann will get one hit on Ruggle as he charges past.
Tartann knows that Sylvianna shouldn't be interrupted, she has a low AC and very few hit points left from the previous battle. He cannot let Ruggle get to Sylvianna. He decides to shield bash Ruggle.
Ruggle's AC is 14 (+2 armor and +2 Dex bonus) his combat maneuver defense (CMD) is 12 (10 +2 Dex). Tartann makes an attack and the total is 21. He hits Ruggle with his shield bash doing 5 points of damage and he gets the free bull rush attempt from his shield slam feat. He uses the 21 from the attack and +4 from his improved and greater bull rush feats for a total of 25 on his combat maneuver check, 13 over Ruggle's CMD.
The combat maneuver succeeds throwing Ruggle 5 feet plus 5 feet for every 5 points over Ruggles CMD. The total is 15 feet. Normally Ruggle would fly 15 feet and be able to finish his movement but there is a wall 10 feet away so Ruggle hits the wall and falls flat on his face (Prone).
Ruggle uses the rest of his round standing up from prone.
Tartann has successfully stopped Ruggle in his tracks!
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This is one example of how the Shield Bash/Shield Slam can be used in combat but there are a lot of tasty battle scenarios where this can come in handy!