Soldier of Fortune 2
In game press Ctrl+Shift+~
Enter the following command:
bind H "hud off" (or replace H with any other preferred key).
After binding key, press it to hide hud. Or, just type "hud off" in the console. The setting does not stick, so must be re-entered each time you play, or just press the key you bound to the command "hide hud". Binding will hold.