Traditionally, the fulcrum refers to the part of a percussionist's grip that is the main lever for the drum stick to rotate.
If one consciously locks their wrist, elbow, and shoulder so that they remain stationary, the only degree of freedom left to move the stick is the finger lever.
If one were to hold their sticks or mallets with a 'death grip' while using only wrist rotation, there is the possibility of tendinitis or carpal tunnel syndrome occurring.
In general, the forearms will move slightly as a reaction to the forces the wrist and fingers are putting on the sticks.
If one then freezes the wrist and finger levers they can move their stick, hand, and forearm by rotating at the elbow.