The smack and hack is one of my favorite covered entry techniques. It works very well as a blast against an imminent threat, as a defense against a straight punching attack, and as a counter to some grabbing attacks. The smack and hack not only has the potential to instantly knock an opponent out, but it also leads to a great control position, the head and arm control, from which you can use strikes, locks, throws, and chokes from a position of safety. You can see video of the smack and hack on my techniques page. Below are images with one follow up example:
See more self defense techniques.