Launder the shirt as normal in the washing machine per care label instructions.If it is safe for the fabric, launder the shirt in hot water.
Add 1/2 cup of baking soda, which absorbs odors, to the washing machine at the beginning of the wash cycle. Use baking soda in addition to your regular laundry detergent, not as a replacement.
Smell the shirt after it comes out of the washing machine. If it still smells like paint fumes, launder it again, but this time, add an appropriate amount of laundry detergent and one cup of white vinegar, which also has the ability to absorb odors.
Hang dry the shirt outside or hang it up to dry in a well-ventilated room to remove any lingering paintball odors.