Combat rating is determined by a variety of factors, including your environment. It is the determining factor whether you hit or or your opponent hits more. The higher your combat rating the more you hit and the less your opponent hits you.

Variables that affect your combat rating include:

• Fighting skill
• Normal fighting (a sub skill to Fighting skill)
• Kingdom bonus*

* In the case of kingdom bonus, this would only apply to Wurm Online's Elevation and Chaos servers/maps. As far as I know Mythmoor has no kingdom bonuses that affect combat rating, but if they did here is how it would work. 1) You would receive +1 combat rating if less than 20% of the server is online, 2) If your kingdom constitutes less than 10% of the server population then you would receive +1 combat rating.

Rolf's forum post:

Every creature has [a combat rating]. It is very similar to the concept of levels in other games, just that it fluctuates a lot more in Wurm. It is the basis for calculating the chance to hit another creature. Players have a base combat rating of 4. If the troll I am fighting has CR 10 and I have CR 4 I have about 4/(10+4) chance to hit the troll, or 29% every attack. The troll on the other hand has 10/14 so it'll hit me 71% of his attacks. Very simplified. There are parry bonuses and covers involved in that specific algorithm. Also your basic fighting skill is added 1 per 10 in skill, so if you have fighting 59 you have a CR of 4+5.9=9.9 in base CR. Monsters have their type modifying base CR, making Champion creatures have maybe double the figure of the standard type. A lot of things also affect the combat rating before that algorithm. Things such as footing, if you are prone, certain combat moves affect it negatively, being flanked, height distance to target, focusing, being drunk.. things like that. And also the kingdom bonus. Now, in Player versus Player combat the base fighting skill is added 1 point per 5 in skill instead, so a player with 99 fighting skill would have like 23.98 in base CR and one with 50 fighting skill would have CR 14. So how much is the kingdom bonus? The kingdom bonus is 2 if your kingdom has less than 10% of the server population. It is 1 if the kingdom has 20% or less of the population.