Well, it looks like we’re needed for some intimidation. A [ random ] person has been causing trouble. He’ll be at a [ random ] location too. Go out and talk to him–he will refuse to be intimidated. This will start a fist-fight.
Like any fight, dodge out of the way when he swings and clock him back. You can even hold the attack button for a power attack. Chances are you are a LOT tougher than him, so you will knock him down for good before too long. Talk to him a few more times and the fight will be over.
Go back to Jorrvaskar and talk to Farkas to tell him you’re done. He’ll give you 100 Gold as a reward, and the quest will be done with. He will then say that Skjor has another job for you, starting the next quest: "Proving Honor".