Perhaps the M.D., Ph.D. was too sore to walk the next day and couldn't go to the office and overcharge the people that had an appointment that Monday. The lawsuit may be the M.D. trying to recoup the lost income in another way.
I hope the lawsuit goes to a jury trial and the lawyer for the race director can ask the M.D. about the doctor's billing practices. Examples such as padding the bill and charging inflated prices for "intensive consultation" (5 minutes of asking what exactly is wrong) should be brought up in front of the jury. Overcharging and charging for phantom services can bring the income up high enough where the M.D. can afford to enter the Suzuki marathon.