Attacking Aegis

Requirements: Proficiency in shields
Your skill with using a shield allows you to embrace both defense and offense. 
While wielding a shield and no other weapon, you are able to attack using your shield, dealing 1d8+STR per attack. 
Additionally, you may spend an attack attempting to pin an opponent to a surface using your shield. Choose a target within 5ft of you that has a size equal to or less than yours. The target makes a DEX or STR saving throw (their choice), attempting to either dodge the strike or push it back. On a failed save, they become restrained, and may spend an action attempting to free themselves. If the target is next to a wall or other flat, vertical surface, they have disadvantage on the save against the pin. If no such wall exists, you instead attempt to shove them to the ground, attempting to restrain them from above. In such a case, they have advantage on the save.