You have to be faster then your opponent. down O fully charged on the ground. but the nearly impossible part about this... it only works if your opponent is behind you when you release down O. Your opponent well get knocked above you were, you well have a small window to hit with jak's lv 1, and he well have a small window to evade.
So its highly situational and probably very unreliable. While I'm glad a way to combo into super does exist for him, I think my point still stands.
Yeah people don't use Jak or Big Daddy at all but I'm glad. When I get a victory with Jak, it feels so rewarding! Also him being my main I can use him pretty well. I think I can get wins so easily against even the best players/characters because they aren't used to fighting Jak and I have pretty much grown accustomed to fighting drake, raiden, kratos and sackboy. Try using Jak's level 1 as a tech trap or anti-air but as an anti-air you have to do it a little early so you don't get hit out of it. Sorry for all the extras, I just wish people could see that even though a victory with Jak is hard to obtain, he is still worth playing.