User blog comment:Jasca Ducato/Assassin's Creed III - My Review (Xbox 360)/@comment-82.73.209.137-20121112144717/@comment-4975789-20121112170315

Not sure quite what you're describing but it's either a double counter or a tool counter.

To do a tool counter, press B as the exclamation mark appears above an enemie's head. When time slows, press Y, and you will use your tool to counter (e.g. gun, ropedart). To do a double counter, you need to be lucky and have 2 enemies attack you at once. An exclamation mark will appear above 2 enemies, and you simply hit B.