You want to block it when it's very close to you, and try to release block the instant it touches you, you even have to do this offline. It's not unpunishable, but when you play, you get into a groove where you know exactly how to counter it. You want to make sure you get a F+Run+Attack out on it. I use the slide a lot, but often times when someone is jumping, and very often I'll hit it so they land on it, and it flips them the opposite direction. It's all intentional.