I really don't understand why everyone here doesn't have Krud Kutter in their house by now.
I've been answering these kinds of questions for years (paint, stain, food, crayon, grout, bath scum and on and on) amd the answer is always Krud Kutter.
It's in the paint thinner section of Home Depot but all natural, non harmful, no fumes. Delute with water for walls. Use full strength for really nasty tubs, wood work, even in place of bleach for your whites. Removes red clay, grass stains, blood etc. Never found a surface or stain it didn't work on and it doesn't5 harm the orginal finish.
It's the only item you need in your cleaning bucket for your cleaning business, too.
(I do not get paid by this company)