Perhaps. As we known, a concussion is a traumatic brain injury, which is mostly caused by a direct blow to the head, such as a fall, a car accident, or being struck on the head with an object. But a concussion can also develop due to body blows that snap the head forward or backward. If the hit in the eyes are violent, then the concussion can occur.
Yes, I think it is possible. A concussion is caused by the significant blunt force on head. It is close-head injury but not lethal. Usually a concussion would cause a finite period of unconsciousness or memory loss. A mild concussion won't cause unconsciousness or a very short unconsciousness, named as blackout. So if the hit in the eyes is significant enough, it is possible to have a concussion. Just like boxing, a heavy blow in the face would probably causes the people black out or even lost consciousness. If it is not so significant, it might just left the black eye by hitting in the eyes.