Hammer Driver, called Snake Fang (スネークファング Sunēku Fangu) in Japan, was introduced in Tekken 3. Its reach seem to implicated that the move is entirely a defensive counter attack, as the first part of the move has no chance of connecting with a simply standing opponent, and if the first part whiffs, the opponent has plenty time to block or evade the second part of the move. If the first part connects however, in case of the opponent attacking or simply moving into it, the second part is guaranteed.
When to use
Hammer Driver is a good weapon against players who try to rush their opponents or against pokers (people who jab often). For this reason, it is a good choice for switching from defense to offense.