You can get this on the "Face Off" level from the hero campaign in a couple of different places:
1) Just after you drive the truck across the bridge, you'll see a small group of four goons on the left of the screen. Keep going right just a little bit, and you'll trigger another small group of goons. Both goon groups will swarm you, and there are enough of them to get the achievement if you're fast enough. Make sure to wait until they're all right on top of you before you start attacking.
2) During the battle against Two Face in the bank vault at least one group of eight goons will attack at some point during the fight.