This is an excerpt from a fantasy novel.  In this scene, Kilen (the swordsman) is chasing down the Kopi, a man who has been hired to guide a group safely through a dangerous forest but has fled the group and is escaping into the forest.  Kopi is the name of the character’s ethnic group.  Farce is Kilen’s horse, and Tegu is Kilen’s sword.
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The Kopi saw the swordsman bearing down on him and whipped the reins against his horse’s neck, but Farce was faster and brought Kilen to the fleeing chestnut’s flank.  Kilen gripped Farce tightly with his knees, switching the torch to his left hand and drawing Tegu with his right.  Now he held the torch in the hand away from the Kopi, the sword towards him, and he swung his arm forward, connecting his fist with the back of the guide’s head. [This is a very good, strong start to your scene. Immediately I get a sense of motion, conflict (pursuit, specifically), and the characters. I don’t have any sense of where they are, but that may be in the paragraphs leading up to the action, so that’s fine. The final sentence is a little confusing to me, because he’s holding a torch in one hand and a sword in the other, so which fist does he use to hit the Kopi? It’s clear in the next paragraph, but you might clarify it here. You might consider combining the latter two sentences to avoid the reiteration about the torch and the sword and set the scene a little at the same time. Consider as an example: “As Kilen drew alongside the fleeing Kopi, his torch fluttered and hissed like a flag. He gripped Farce with his knees, drew Tegu, and swung the pommel at the back of the guide’s head.”]

With the force of the heavy pommel behind it, the blow pitched the Kopi forward and he lost his grip on the reins. [Divide this into two sentences, because they’re both important points. Give the Kopi a more pronounced reaction to the blow. “With the force of the heavy pommel behind it, the blow pitched the Kopi forward. His hands flew to his head and the reins flapped loose around his waist.] The two horses still galloped forward and a branch whipped across Kilen’s face as Farce went to the left around a large tree, the Kopi’s chestnut to the right. [You’re actually going into a little too much detail here. I’m nitpicking because you’ve got a really good scene. Instead of saying who went left and who went right, simplify. “The horses split apart to avoid a tree, and a branch whipped across Kilen’s face.”] Kilen had just enough time to sheathe Tegu before the horses came back together, and he reached out with his free hand, grabbing at the chestnut’s reins. [Instead of saying Kilen had just enough time, simplify it again and just say “He sheathed Tegu to free one hand and grabbed at the chestnut’s reins.”]

The Kopi had regained some of his wits by now, but Kilen was faster, wrapping the chestnut’s reins around his fist and pulling with all his strength on the bolting horse’s head, at the same time sitting back hard, signaling Farce to slow his pace. [Okay, this is a really busy sentence. Break it up into a couple of shorter sentences and simplify, simplify, simplify. Don’t give your reader too many things to keep track of when you’re blocking out a scene. Too many details will bog down the action.]

As soon as their breakneck flight had slowed, [I don’t like your use of “had” here or in the previous paragraph. Don’t use past perfect tense in an action scene because you want it to have a feel of this is happening right now, not something happened a few seconds ago and I didn’t tell you about it. 😉 ] Kilen flung down the torch and wrapped both arms around the Kopi, pulling him from the saddle.  The guide rolled free of the horses’ legs and scrambled to his feet, but not before Kilen’s feet hit the ground.  The Kopi turned to run but Kilen pushed him down again, and stood over him. [This is a good Stunt here. Nicely done.]

The torch gamely blazed on in the undergrowth, oily rag resisting the rain, and Kilen stooped to retrieve it, his eyes on the guide.  [I’d break up the previous sentence into two. As a general rule, if you have any sentence with more than three clauses, it should really be two sentences.] “Get up,” Kilen said in his native language, hoping that it might be close enough for the man to realize what he was saying. [I’d end the sentence with “Kilen said.” and leave the rest off.]

When the guide didn’t move, Kilen reached down and grabbed the Kopi’s collar, dragging him to his feet.
“Let’s go,” Kilen said, giving the man a little push to encourage him, and whistled for Farce.  [Again, I’d break this sentence into two different sentences. Make whistling for Farce a new sentence.]

The Kopi stood silent and miserable while Kilen collected the chestnut and tied her to Farce.  Farce was sidling and prancing, begging to continue their game as Kilen prodded the Kopi over to Farce’s side and wordlessly had him mount.  Kilen swung up behind his hostage and their combined weight managed to quiet Farce.  To Kilen’s relief, it was easy enough to follow their backtrail to the camp.

[You’ve got a very good action scene here, and I think you’ve handled it very well. You asked me specifically about how to avoid overusing characters’ names and in this circumstance, unfortunately, it’s difficult since you have Kilen (male) and the Kopi (also male) and Farce (undetermined but I suspect male as well). You can’t use the pronouns he and his without potential confusion. On the other hand, you can use alternative descriptions instead of names: The raven-haired swordsman; the fleeing guide; the stallion; etc. My final advice for you is to simplify your sentences – you’ve got a lot of multiple-clause sentences that could be split into two or more. Also consider whether you may be force-feeding too much information to the reader to the point that it slows down the pacing. And get rid of those pesky adverbs and watch out for passive voice, especially in the last paragraph. Thanks for your submission!]