Shield Slam - As a bonus action, the shield bearer can slam their shield into a target.  Roll a STR based melee attack.  On a hit the target takes 1d8 bludgeoning damage and must make a STR saving throw or be pushed back 10 ft.  The shield bearer can elect to push the button to release the springs built into the shield.  If they do, the increased impact of the shield deals 3d8 damage and the target is pushed back 20 ft. and knocked prone.  After the springs in the shield have been used, it looses it's AC bonus until they have been reset, as the sheild dangles loosely from them.  Resetting the shield's springs takes 1 action.