This codepointer declares the calling player dead and causes the player "weapon" state to jump from its place in the FireHands state sequence to the corresponding FireHandsLower state. (For example, if the player weapon is in the FireHands+2 state, it will jump to the FireHandsLower+2 state.) This will only work correctly if the player class declares the FireHands state sequence first, followed by the FireHandsLower state sequence, and with exactly as many states in both sequences. Notably, it means that inheritance cannot be relied upon: if the FireHandsLower state is redefined, then the FireHands state needs to be redefined as well, and vice-versa.
Note that it changes the "weapon" state, not the "player" state, even though it is not meant to be called from a "weapon" state.
This codepointer is restricted to StrifePlayer and actors inheriting from it.