Man pages matching name sdl_joysticknumballs in section 3:

SDL_JoystickNumBalls.3.en	debian 10 / libsdl1.2-dev
SDL_JoystickNumBalls.3.en	debian 11 / libsdl1.2-dev
SDL_JoystickNumBalls.3.en	debian 12 / libsdl1.2-dev