I don't think any of you know what spawn trapping is, batchynator was right, it's part of all FPS games, but there is a difference between spawn trapping and spawn killing.
Spawn trapping is dominating the key points of the maps, letting you get kills by cutting the enemy team off from getting strong weapons.
Spawn killing is killing people the moment they spawn.
Spawn killing is bad, and you will get banned eventually, spawn trapping is perfectly fine.