Making a fist in karate is one of the most important things you will learn when you go to your first karate class. If made correctly, your fist becomes one of your most valuable weapons in karate, if done incorrectly; you may end up with broken wrists or a broken thumb.
Stage 1: If you simply start with your hand open, with the palm facing you. Ensure your fingers are tight together, with your thumb stretched out from the rest of the fingers. The fingers from this point roll backwards in two phases.
Stage 2: First, the tips of the fingers roll inward.
Stage 3: Then the fingers roll inward again until your hand is tightly clenched together.
Stage 4: The final stage in making a fist involves bringing the thumb tightly across the fingers.
It is important to keep the fingers tight together, with the thumb stretched securely across the fingers. If your thumb for example is not securely stretched across, but sitting loose, the thumb may get caught on for example a gi top and get broken.
Another point to remember is when striking a surface using your fist, ensure only your seiken (first two knuckles) make contact with the target, not the entire surface of these two fingers, for the fingers will easily break if pressure is applied to these fingers, whereas the knuckles can deal with the shock of impact.