On spigot 1.11 PS 1.11 people can kill other players and animals on fileds event with protect animals flag and no pvp flag using flaming bows.

If needed I can make short video as proof.

Please try
/ps insert no-projectile-throw
inside one of those fields, if it dont work you will need to
adjust the field flag's list in config.yml and add the flag there.

I forgot the command to insert this flag into all fields of a
type that are already placed but there is one

no-projectile-throw: true
prevent-potion-splash: true

All pstones with those prevent arrows/splash potions inside
or from outside to inside the field. Works 100% against non allowed.