Lamisil AT is the best/strongest OTC cream for ringworm. The product states that it's for athlete's foot, but it kills the "tinea" family of fungi, which comprises athletes foot, jock itch, and ringworm.
You don't neccesarilly need to go to the doctor for ringworm; a common rule of thumb is to go to the doc if you get ringworm on your face or in multiple areas.
If you need stronger medications the doctor can prescribe oral Lamisil or Diflucan(which is also prescribed to treat yeast infections, which is also a fungi). When applying the cream, make sure to cover not only the ringworm itself but a little bit beyond because the infection spreads/grows outward (in an expanding ring).
It's very important to always shower after training and always wash your workout clothes after any type of grappling. It's important to instill this in your training partners/teammates as well.
After all, ringworm is the least serious skin infection you can get from grappling. Staph and the dreaded herp are out there as well. If you get one of those you HAVE to go to the doctor. MRSA (antibiotic resistant staph) is becoming more and more common.
MRSA is almost always treatable with the stronger and newer antibiotics such as Vancomysin, but there are cases where MRSA has killed healthy young athletes.
Dandruff shampoo is also a good suggestion for its anti-fungal properties. Go with Selsun Blue or Nizoral over Head and Shoulders, as they have stronger active ingredients. And you can apply it over your whole body and not just your hair.