I think I knocked out my brother-in-law.
How is it that you were in a position to knock out your brother-in-law?
He started a fight with me and I finished it.
The use of violence is never good especially against someone in your family. Try to reestablish peaceful relations with your brother-in-law.
He deserved it and he won't start trouble again.
Sometimes you do have to defend yourself, but overall, violence is never a good solution. Hopefully in the future, you and your brother-in-law can settle problems with words and not fists.