Can someone help me with the Assassin's Creed Brotherhood multiplayer, please?

Alright, well I absolutely love the AC series, but I recently started playing the multiplayer (only lvl 7) & I'm a little confused. Sometimes when I go kill my target, they throw a smoke bomb, "stun" & kill me. I don't know how to do this, & I really want to. Some people find it boring, but I actually enjoy it. I just think it's a little confusing. I play on the PS3 & am trying to get the platinum, so I want to make sure I get the multiplayer down packed. I think you have to be on a higher level to stun your pursuer, but I just want to make sure. Thanks, guys.