enemy spawns

Okay, you take back an enemy flag that's actually the one closest to your base. You check it out, you walk around, peeking around corners, you want to find a radio beacon. Okay, there's none! Ohhhhh!! Suddenly, just as you've made the decision to move forward with the other flag, out of nowhere, 40cm away from you, an enemy team spawns behind you and you die. You don't understand if they're teleporting, you don't understand where they're coming from. Especially because the game wants to punish you!

Why do these people without a beacon, without a player who allows them to spawn, and without a flag spawn behind me? Can anyone please explain this to us?