Here's a video of me doing it to show how toxic this is:
Now, I'm not going to say I haven't partaken in this, but every high-level player I can think of has too. Also, I'm aware this was a thing in I2, but still... Here's the strat:
When they have 1 wave left, run to their spawn point. When the next wave respawns, the restricted area limitation is lifted, and you can bomb them, shoot them, etc.
My suggestion to fix:
Keep the restricted area for 30 seconds longer after the last wave spawns. Easy fix.
It's funny, but detrimental to the game.