k.d

With four boys, I have a lot of experience cleaning uniforms. : )
I've tried them all and the best that I have found is a product called "Iron Out". I found it at Kroger but I'm sure other stores carry it. Look in the cleaning supplies.... not necessarily with laundry detergents because it was intentionally made to remove rust and iron. It is in a bottle but when you pour it, it's actually a powder. I run warm/hot water in the washing machine and pour some iron out in... then soak the uniforms for about 10-15 minutes. Then I add detergent and wash as normal.
Our entire baseball team uses it now and it does wonders!

Oxi Clean and LOTS of spray and wash! They've renamed it Resolve for clothes or something, but use the Spray and Wash brand -the bottle is still the green and red. Saturate the red clay stains with it and pour a lot of Oxy Clean powder into the washer with the clothes. Wash on HOT. This always does the trick for us with red clay.

Oxy clean is the best! I make a paste out of it and rub it on the stain and leave it for a day or two if necessary. If the pants are white it will probably work like a charm, if they are colored, it might discolor it just a titch if you leave it on too long.

What I was told our local professional team uses on their white pants is Simple Green. You can get it in the automotive section of Wal Mart. The moms that used it on my sons team had great looking pants. I will be getting some and using it.

Someone just told me this the other day, but I've never tried it. Simple;
use any spray bottle and fill half way with the plain Dawn dish soap and the othr half with water, shake, spray, set and wash in regular detergent. Try it, at least it's not expensive. Let us all know if it works. Good luck.

I know of a natural product that will remove lipstick, magic marker, tree sap, chewing gum, etc from clothes. I bet that it will remove red clay.

Not sure about red clay? But when my son gets that really, really nasty baseball field dirt & sliding stains on his uniform, someone told me to hand wash them with dishwasher detergent. (Rub it on & in) But maybe wear gloves when you do it b/c it's pretty harsh on your hands.