If you let me get to the enemy base in a teams game, I shall take any opportunity I have to use this time to win. It is your fault, really. If you don't want people going there, then fix your map. I will be on the outside of whichever boundary you place. If you have one single exit from the base, then I will shoot at that. If you then open the door and let me in, I'll start killing people. I'm not going to arbitrarily let myself die because you want me to stay outside of an 8000 feet radius of anywhere you happen to be. (in which case, I'll get a sniper rifle and fire at you) If you leave a hole in the wall, I'll fire through that.
You have a steady supply of team-mates against me, one person. Plan something - press the Y key. This is a private team chat. Use it.
When you spawn, you have 2.5 second of complete invincibility from damage. Use this. Get a gun. Fire at something. Don't just stand there, take it and then complain.
Having anti-spawnkilling rules is stupid because it's basically you, the mini-game owner, at fault for making it wrong in the first place.