Red dirt in plaid shorts...please see inside .?

well my hubby wore his plaid very nice shorts today and ended up playing soccer , well when he got home there was red dirt all over the back and sides of them where he slid and so on , what is the best way for me to get the red dirt out with no stains left ? I actually have them soaking in cold water with some hydro max ariel oxy azul liquid detergent whicg is the best stuff i have ever used to remove stains , but i just do not wanna mess up these shorts please help and thanks