I think JOK got the head injury in the house.
For me, the question is…why?
Maybe BH is a psycho and wanted revenge
Maybe CA is a psycho and wanted revenge
Or…maybe JOK knew something/had info and BA thought he was a rat
Or maybe John started something with someone over someone else the second he got in the house and a little punk and a big dog got involved to help out and things went badly very quickly?