Hello,
When playing a game in fullscreen mode, Xscreensaver doesn't seem to
be notified that there has been user input from the keyboard and
joystick, so it will activate after a little bit of "inactivity."
It should definitely be poked if there have been:
Key presses
Joystick button presses
Mouse clicks

Xscreensaver probably shouldn't be poked if a joystick moves, because
of deadzone confusion and high sensitivity.

Of course, a user can disable xscreensaver, but that's a pain in the neck.
Windowmanager used is Fluxbox.