Yo! I have a few tips about combat in freeform roleplay that might help you:
1. I find it useful to decide on the outcome with your partner ahead of time. That way, not only you can focus on writing an interesting fight, but having the same end goal your partner has makes it easier to know when you're going too far, lets you accurately judge what kind of damage your character can deal without going overboard and allows you to focus the scene towards a tangible climax. This approach is more focused on story building than the "game" aspect, as it's less spontaneous, but it's worked wonders for me.
2. If you use a novel format, don't write pretty in a fight scene. Write simple and fast. In creative writing, using simple, strong sentences and less description puts more focus on the action and "speeds up" the pace of your writing, both in style (by giving the frantic feel of combat) and output.
3. If you can get your partner(s) to agree, you can use online coin flips! You can use these to quickly and simply decide the outcome, whether or not hits land, etc. It doesn't involve complicated stats, so it might be easier to convince partners to adopt the convention.
4. Some RPers use reply speed to determine what you can do, which is more... real time, I guess? Like, how many hits you get in or whether you can block is determined by whether you can post before the other player. But if you're on the slow side, like me, this convention... does not work. Heheh.
The important thing to remember in freeform RP is that communication with your partners is everything. Ideally, you should be able to judge how a fight would go based on what you know about the characters involved and write based on that. Freeform RP is a lot less like a game than RPGs -- it's closer to writing a story.