Grade: B / C
Open the console in game with ~. Type g_showHud 0.
If the setting holds with restarts, you're done. If it doesn't, edit the file: Quake4\q4base\Quake4Config.cfg
find the line:
seta g_showHud "1"
change it to:
seta g_showHud "0"
You can also use the command: toggle g_showHud
That will turn it on off with a key press. To bind it to a key, open your console and type: bind h toggle g_showHud
Change 'h' to the key of your choice.