Xonotic

Here is a suggestion how to solve that problem/manage the "spec-and rejoin problem", out of the thread:

• Pressing F3 as soon as you fall off into the void WILL put you into spec mode, but only the moment you've hit the Trigger Of Hurt (or a lost rocket/nexbeam/blahever kills you).
• Pressing F3 when you're standing still WILL put you into spec mode immediately.
• Pressing F3 when you're in mid air after a jump or shot WILL put you into spec mode as soon as you hit a surface.

As far as I recognized there is already a delay of 3 seconds before getting into spectator mode. Could perhaps be improved, on a map like Space_elevator its still possible to avoid falling off the map by pressing the spectator key early enough.

Maybe, after pressing F3, the server sets the players score to 0. Then when the cheater rejoins they will have to restart.

Or detect the cheating and announce to the server that player X is cheating, then add a waypoint over their head "I CHEAT", add a special marker to the radar map, any homing missiles will automatically hit them, they take more damage, their max health is reduced and some other punishments.