Spawn protection prevents players from building in spawn, undoing any attempts at placing or breaking blocks. Players who have any operator level are able to bypass it and build anyway. If there are no ops on the server, then spawn protection does not apply. Spawn protection only applies in the overworld. Spawn protection does not apply in singleplayer.
spawn-protection field in server.properties determines the side length of the square spawn protection area as 2x+1. Setting this to 0 or a negative value disables the spawn protection. A value of 1 protects a 3×3 square centered on the spawn point, 2 protects 5×5, 3 protects 7×7, etc.
|?||Added spawn protection. The radius is always 16 (protecting a 33×33 area).|
|Spawn protection no longer applies if the server does not have any ops.|