Links to rules aside, there are actually several differnet types of RC Combat. They loosely break down in to 3 types. Streamer combat (usually with glow-powered planes), full contact combat (with Zagi-type electrics or slope gliders), and electronic combat (usually with a particular vendor's combat modules on electric park flyers).

Most combat, as far as I can tell, is flown informally, just guys getting together, deciding on their own rules (or lack of rules) and going at it.

The most organized national combat organization is the RCCA, which is focused mostly on glow powered streamer combat. There are several classes listed under RCCA rules.

A couple of action shots from contests around here: