Probably the coach was not playing a doubles match at the time.
Very few players get hit in the face, as the body has a natural reflex action to protect head parts, and certain body parts.
Coach was probably feeding balls or otherwise distracted, and a stray ball came his way out of his sightline.
If you're good enough to play net position, your reflexes will protect your face.
If you don't belong up at net because you can't volley or defend yourself, well, maybe you shouldn't be there and you placed yourself in harms way....your fault.