DISCLAIMER: I am not responsible for any injuries from paint in vital places (eyes, mouth etc.) or property damage from paint. Make sure it is okay with the people you are playing with and the owners of the field that you are using this.
Step 1: Materials
sling shot sling
old cup or container
washer (sling should fit inside)
nail or other small metal rod (I`m using an old allen key because it looks cool)