I usually play airsoft on a remote piece of government land. A few days ago, a Highway Patrol Officer happened to be driving by. He talked to my dad (I was pwning people with a P90 at the time) and told him that it was perfectly legal to play airsoft their, but that firearms rules apply.
To play legally you:
MUST be 150 yards from any roads when shooting.
NEVER shoot across the road.
I recommend that when possible, you play at an actual airsoft arena. If you have difficulty getting to an arena like I do, pleas make sure you play legally. Have an orange tip on your gun, and obey other rules stated, and it could be a good idea to notify authorities of what you are doing.
*Please add any thing you should do when not playing at an arena, or other laws.