Depends on where the backyard is located.
no
Only if it is legal. :)
No
No
i think so
No.
Laws on this vary by jurisdiction.
No. Because, in order for you to shoot them you would have to get their permission to shoot them. If you accidentally shoot somebody inside your backyard without their permission, it is their fault for being in the yard with someone that has a paintball gun and is shooting it in the first place.
yes
As long as you dont shoot anything that does not belign to you, including your neighbors land.
it's fine to shoot an arrow through a bow as long as it doesn't kill any body and you have a target to shoot at.