Face Smash
This is basically a clawed hand palm strike and is also known as the Tiger's claw. The hand is held as if holding a grapefruit and the strike is delivered in one of two ways.
Method Of Practice
The first is straight into the face in a piston like fashion off the lead or rear hand, as if throwing a straight left or right punch as a boxer would. This was the original method that was taught by W.E. Fairbairn who said that when facing a frontal attack, your best option is usually the Tiger's claw. The strike is combined with a forward drop step allowing you to put your body weight behind the strike.

The second method is best used from a hands held high submissive looking fence. The striking hand is held with the fingers spread as if holding a grapefruit and is delivered straight down into the face as if throwing a baseball. At the same time, you vault forward off your back foot to propel your body forward and into the strike, driving your hand through your target as if trying to touch your own knee. In both cases the aim is to smash the palm into the attacker's face with your fingers curled and spread to maximise the chances of reliably impacting the eyes.

Face Smash/Tigers Claw
The lead hand straight piston-like strike, similar to Fairbairn's method.
The straight down, throw the baseball method with arm check. Note; both methods are accompanied by an explosive forward drop step.
Although this strike is intended for the facial area you need to understand that the idea behind it is simply to deliver the maximum amount of impact to target area in order to shake the brain and produce a knockout therefore the target area for the head is generic meaning any where that you strike the head as long as you accompany it with sufficient impact, will do the job as the example below will show.
Push/pull to face smash & grab:
Use a fast push/pull to spin your opponent whilst keeping a hold of him and placing your arm horizontal with the point of your elbow in his back.
From here grab the scruff of his neck and rag him backwards as you push with your elbow to break his structure. Drop your head and control his exit.
The option is open to use a face smash or Tiger's claw strike to the back of the head if the threat dictated such action.