Anytime you are carrying a paintgun in a 'safe zone' such as the parking lot or staging area where people are not wearing goggles, you MUST have a barrel plug in the barrel. Know the rules of the game and abide by them. Never remove facemasks or goggles while on the field. Do not play when very tired or hungry. Bring food or money to buy food from field.
Most injuries occur at the end of the day when players are exhausted.
Not even with protection. If barrel needs checking remove from the gun and check. Notify the field owner or manager of any medical conditions, allergies etc. Not really, but it will help. As with all strenuous exercise participants should stretch and warm up before playing.