Based on how I play, I usually start defensive first, and when they’re full-screen, I go offensive, continually pushing them into the corner until I’m in the right position to start his corner trap.
When you’re forcing them off your ass, use these any of these anti-airs accordingly- c.HP, c.MP, j.HP, RC Spinning Ball, HCB + LK, HCF + any K. When they get too close to you and you’ve been knocked down, mash on c.lp on wake-up. If they don’t block, you’ll do a 3-4 hit jab combo into ball swing and knock them back so you regain momentum. If they do block every jab, follow up with a roundhouse or a slide.
Offensively, when you’re rushing somebody, you want to send Choi out first to bait any mistakes (prefereably his HCF + K), and do an occasional slide. When you knock them down, do Choi’s HCF + HK, and if they block low, low jump and hit HK. Choi will connect, and you can combo into a rush super. In addition to that, Chang’s command grab is a very nice move to tick with. So if they’re really good at blocking, you can low jump in with nothing and do the command grab upon landing.
And finally, when they’re cornered, you trap them. Do Choi’s hurricane cutter (HCB+K), and mash HP before Chang finishes his thumb-up pose to go right into the ball swing. If they attempt to do anything in between each hit, chances are they’ll fuck up and get knocked down. This is when you cancel the ball swing (3P) and reset the trap by throwing out Choi again. If done at the furthest distance, you can still hit them with the very tip of the ball and reduce the effectiveness on most counters, like wake-up DPs or ACs. This is not inescapable, but it’s a pain to deal with no matter what groove you’re in. The biggest thing you need to worry about is a wake-up Lv.3 super. SO, when you have the meter, DO NOT forget to do the Choi super! And keep mashing on HP to go into the ball! Be sure to take full advantage of the situation with each gaurd crush too.
And as a general rule, try to get used to Chang’s laggy pokes, notably, any of his HPs.