Use a trigger_mulitple flagged to be team specific. Target the trigger to a Target_kill entity. If you want to add a sound effect or some other scripting function, you can also name a target_script_trigger entity (I think that is it, I have to double check). Use the same targetname for both the target_kill, and target_script_trigger and the trigger_multiple brush will trigger both of them at the same time.
In the target_script trigger give it the scriptname that you want to run, and for the target, the name of the trigger scriptblock you want to run.
I use this in Praetoria to kill cheaters that might use a double jump or a push to get inside the bunker and try to blow the radar controls before the tank has blow any of the entrances. The trigger multiple will instantly kill them, and the target_script_trigger entity calls a script that plays the “HUMILIATION” sound effect from Quake3.
You can also link this to a func_timer so that the killzone is only active during the allies spawn times. But that might just be a little overkill since most spawn times come every 15-20 seconds.