There is only one rule... you can't shoot through enemy spawn/teleporter room shields. In all seriousness though... I have noticed a sudden surge of sub BR 10 players on Mattherson (was there an ad campaign I missed recently?) that definitely don't understand that the door shields allow fire in only one direction. This has resulted in a mountain of bodies that had been bravely standing like Rambo in front of the door unloading bullets harmlessly into a shield while they get torn apart by the enemy faction. While I don't think you should have to spoon feed all game mechanics to new players, perhaps some sort of heads up for obstacles such as this (lookin at you SOE) would improve the new player experience... just saying. "Glowy doors are racist, they only let you and your bullets through if you're the same color as them"