This is the problem with being familiar with the mechanics of a sword fight: you end up describing things WAY TOO MUCH when (re)writing combat scenes in your novel. Yes, it looks really, really cool in my head, and will wow about .05% of my intended audience, but honestly, it's too much for most people. I like that I can visualize, block out and dissect a combat sequence in my brain, but sometimes it gets in the way. It's easy, as the writer, to sit back and go through every option in your head, to play around with three different counters and several different actions (as well as all the footwork and body mechanics and blade work and angulation and... you see some of my problem here :), but this isn't always the best answer. In fact, it can be a train wreck if you aren't careful.
A current example: my protagonist is a poor swordsman at best, more street-educated that classically trained with weapons. This means he isn't always pretty, doesn't always make the right choices, and relies on a blend of skill, strategy, street smarts and luck to pull his bacon out when things get tough. Sometimes, this is in direct contradiction to my own instincts and skill set, which makes things interesting. It also means that my first visualization of a scene may or may not be the best one. There is what I would do, what he should do, and what he ends up doing. Sometimes all three align, other times they completely diverge. It's the latter, more common development, that tends to cause me the most trouble. Some days, I think it might be easier if I didn't study historical sword fighting.
The best answer I have found for this so far (aside from frequent rewriting, which can be like pouring gasoline on a slow fire at times) is to actively remind myself how much my narrator does and does NOT know about fighting. Likewise, I try to keep his relative skill level compared to his opponent(s) in my fore brain as well. Just because I know the proper counter to this move, or might try that action, or could see his opponent do this attack, doesn't mean that they will. I need to keep my understanding and instincts at arm's reach, because it's not me doing the fighting, it's my protagonist, and he's going to act and react and fight a lot differently than I would or could. this is true when I am writing about exceptional fighters as well, only from the other direction.
If this sounds like a practice in characterization, it is. And it applies to more than fight scenes. Stick it into any topic you, the writer, are passionate about, and the situation is more or less the same. Your passion and knowledge can inform your writing, but it should not dictate or take over the process. The trick is to take pieces what you know, what you believe, what you feel and love, and find a way that it fits for your character, world and story. It may not be precisely what you hold to, nor even what you envisioned, but if done well, it will still have that underlying foundation of truth that comes from you. That, I think, is where the interest and connection and "coolness" factor that Lyda was talking about comes from. If you convey the passion without all the geeky baggage and mind-numbing details attached to it, it's no longer a geeky info dump: it's something cool the reader didn't know before.
So, what's your geeky passion? Have you managed to fit it into your writing? If so, how? If not, why not? And does that matter to you?