If the hat is stained, use a prewash. Then toss the cap in the washer and wash gently in cold water. … Or wash the hat by hand. Cool-to-warm water in the sink, mild detergent, gentle rubbing with a clean washcloth should do it

People often ask can you wash a baseball cap yes you can however if it is a collectors edition or valuable then it might be better to get the baseball cap professionally cleaned.