Best done with options set to Very Easy, 1 Round, no time limit.
This one is kinda tricky because the opponent
could potentially jump at the beginning of the match if you're playing against AI. Generally, they won't, but if you want to ensure you'll get it with no problems, set up a two player match. A lot of Deadshot's moves unsurprisingly shoot a gun. The fastest move you can do is
. I did this 3 times. Win the match and the achievement is yours.