User blog comment:Gnomeco/Katarina - Should be buffed?/@comment-24087642-20140412063333/@comment-24385282-20140414024702

How to stop Katarina ult within 1 second of its cast:

Step 1: Walk towards Kat who is intent on killing you

Step 2: Get ready to use a CC that has lower range than her Shunpo

Step 3: The moment she Shunpo's she'll start her ult but you'll immediately cancel it

You literally just need to click on her with any targeted crowd control ability, or get ready to aim your skillshot CC on the opposite side of yourself from her, seeing as that's where she'll land when she Shunpo's. CC her too soon? Well, you may not have cancelled her ult but she'll still be stuck right next to you with no resets to escape.