It is worth mentioning that efficiently executed physical violence is far more intimidating than poorly executed melee. If a man can quickly drop another man with a single strike or a fast combination of blows rather than grapple with him, not only will others have less chance to intervene, they will be less inclined to try.
Few people, including the police, have ever been forcefully struck in the face, and even fewer ever want to be. You do not need to learn complicated martial arts moves to knock someone down. You are unlikely to remember the moves anyway in a fight, with your heart pounding and adrenaline rushing through your body.
I would advise you to just practice two or three basic strikes. Work on your speed, power, and accuracy, and aim for the chin just below the corner of the mouth. This is a pressure point, a cluster of nerves, what we call in boxing “the sweet spot”, and you can fairly consistently knock a man out if you hit it hard enough, especially if he is inexperienced or unprepared.