My Son Had Bottle Thrown At Him, Back/right Side Of

My son had bottle thrown at him, back/right side of head. He had a wound that needed a few stitches and a big lump. He has been unsteady since this happened, he almost fell on bottom step of stairs when we arrived home from hospital but now 3 days later his right is teaching, you can actually feel and see it under his eye, what is this?