Combat zone

This is probably a noob question but here goes, Several times I have been in game and the combat zone changed instantly. Being pretty new to the game I get a little confused and usually run in the wrong direction trying to get back into the correct position. I do not spawn camp or ever try to get into a position to fire on an enemy as soon as they spawn, but several times I have found myself in a spawn protected area trying to get back in the correct position..