The thug crumples under the force of your shield, falling heavily to the ground. He's not dead, but he's certainly not making any moves until he wakes up. Speaking of which, there are a few things you could do before then:
Turn the thug in to the nearest Stormwind officers. See what they can get out of him. Wait until the thug wakes up, then try to talk to him. Could be useful. Go through the thug's possessions. Might be something important there.