What is the difference bet
An A rider ( PRO ) is consistently Faster, able to pace a race, extremely confident in abilities, able to avoid mistakes, and is very experience at adapting to changing race conditions.
B riders ( Amateur ) tend to have many of the traits above but lack experience, confidence or drive to go to the next level. B riders have pointed out of the C class by winning races and accumulating results to move to the next level.
C riders ( NOVICE ), Tend to make mistakes, over ride the track or the conditions and lack the experience to put a race together.
In order to move between classes the race organizers put together criteria to measure your placement. as an example riders from one series that can prove results from that series are placed in similar class as the other race series. In some cases A class riders can be demoted if they don't have recent race results.
here is a good reference from the AMA
difference between A
C rider levels?
Enduro
Harescramble
Dirtbike
Racing