There are two major combat clubs.
The NSCC is sport combat. It is a more laid back form of competition. www.sportcombat.rcplanet.com
The RCCA is a more uniform competition geared to a nation wide standard. There are very little C class competitions in the RCCA.
www.scalecombat.com
There are several classes of combat. A class is engines up to .15 cid. B class is up to .30 cid. C class is engines up to .47 cid.
There is a scale class with engines up to I think .26 cid.
If you have any of your old trainer equipment left like an old plain bearing .40 the C class is the best why to get started without buying new stuff. If you have anymore questions the busiest combat forum is on the ********.net site. Go to BOTH of the sites and check it out. To me combat is as much fun as you can have with your pants on