Turn the jersey inside out to attack the sweat stains and prevent damage to sewn-on items such as numbers or patches
Pour 1 cup of white vinegar into the bowl or similar container.
Transfer the vinegar onto the sweat stains, using a sponge or cloth. Don't worry about scrubbing the jersey yet.
Make a paste of warm water and baking soda in an empty bowl or container. "Reader's Digest" recommends mixing ¼ cup of warm water with 4 tbsp. of baking soda. Mix the ingredients with a spoon or your finger until a paste forms.
Spread the paste over the sweat stains on the jersey, using the cloth or sponge. Scrub the paste gently into the jersey with the toothbrush or other brush. The combination of the paste and white vinegar lifts the sweat stains from the jersey without causing any additional stains.
Wait an hour or two for the paste to fully dry on the jersey.
Wash and dry the jersey as normal to remove the white vinegar, paste and sweat stains from the jersey. Leave the jersey turned inside out as you wash and dry it.