Getting your baseball cap dirty can be a pain, especially if it's mold. Mold can cause health complications and be a real nuisance to clean. With the right know how, cleaning the mold off your favorite baseball hat is a cinch.
Plastic hat cages for washing are relatively inexpensive and can be purchased at most hat retailers. They allow for safe washing while keeping the shape of the hat and brim intact. Try putting your hat on a hat cage and throwing it in the washing machine. Run the wash on a regular cycle to get rid of the mold.
If a normal wash cycle doesn't work, try adding 3/4 of a cup of vinegar to your wash cycle to neutralize the mold. The vinegar will kill the moldy smell and the high acidic content should kill the mold spores. Be sure to wash your hat with detergent afterward.
There are a number of different chemical mildew removers that are specifically designed for dealing with clothing. When using these products, be sure to check and see that they won't be harmful to the cloth that your hat is made of.