Doesn’t appear to be a brake-check, just someone having to lift for the kart in front. I concur with the rest of the guys here.
Honestly, I would say that I’ve never seen anyone brake-check another kart before. It’s just not a legitimate strategy in most cases.
Now, I will say at Badger Raceway, the last corner sets up some interesting driving. It’s a tight 180 hairpin and one of the tricks there when defending is to drive in on the bottom “park it” right in the middle of the corner if someone is close to you. They’ll have no choice but to give you a little tap and help you off the corner, giving you a gap. It’s not really brake-checking, more just slowing down mid-corner to make sure you hit the apex with your early entry line. Otherwise they’ll cross you over on exit and drag race you down the front straight.