Fight sequences live in the same world as the rest of your story in the rules of show and don’t tell. You’re going to have to let the sequence play out with an eye for selling it’s believability to the reader. Violence itself can be an intrinsic part of the human experience and everything you write should be trying to keep it in line with how individuals experience the world around them. Here are some tips:
Actions Have Consequences (Character Development): One of the best way to make a combat sequence come alive is to make it integral to your overarching story. This may seem obvious, but it’s actually amazing how few writers actually do tie combat and character development together or use the combat to further their character’s development in the story. The truth is that a fight sequence shouldn’t be treated as an outside force, but as part of the narrative, what your soldier characters experience in battle needs to follow them through the story. It may provide the crux of what inevitably uplifts or destroys them. Their experiences on the battlefield should have an effect on their interpersonal relationships, their personalities, and their outlook. If it’s not changing or affecting those things, then it often comes off as false.
Use these sequences to show something about the character’s experiences outside the of sequence’s necessity in furthering the plot. What do they feel about their own actions? What do they feel about the actions of their teammates? How do they feel about the civilians they are either protecting or whose country they are invading? How do they feel about killing those people?
Actions Have Consequences (Physical): Actions have physical consequences. When someone gets hit in the face, their head knocks backwards or sideways depending on the direction it was struck. They can bite their cheek or their tongue, which leads to blood being in the mouth or feeling pain in the teeth if the person in question forgot to tense or lock their jaw before they were struck. If someone is hit or shot, even if that person is an enemy, the character may notice their physical reaction to the experience. Gun fights in particular are nasty because they are over very quickly and it only really takes one well-placed bullet to put someone down. However, the consequences of a character getting shot should be on the page, including whether or not they have to take the character with them, patch them up, or try to console them in their last moments. Soldiers in particular are trained to think and behave as a group with an eye on the good of the whole, having to make a decision about whether or not they can take their wounded comrade with them or leave them behind to complete their mission, especially if the medical unit is not close by can be a good source of drama.
But whether it’s bullets ricocheting, someone getting punched in the gut, the physical effects the characters have on their environment is important to document to add that sense of realism. So, develop a grasp of physics and body mechanics because they will be important to beyond just word choice and language to selling the sequence to the reader.
Make Use of Your Set Pieces: Acknowledge the environment the characters are fighting in and the challenges it represents. For example, because kicks and knee strikes rely on friction to function, most combatants will be choosy about when and where they perform them based on terrain. The surrounding environment is important to helping the reader connect with the character because they don’t feel like an amorphous blob in a story where you could change where the fight happens and everything would still stay the same. If the character isn’t connecting with their environment, using their environment, their enemies using the environment against them, or finding that the environment is hindering them because they don’t know how to survive in it, then the fight sequence has a problem.
One of my favorite action movies, for example, is the first Die Hard. John McClain is trapped in a skyscraper trying to save his wife from thieves posing as terrorists. You have John’s internal struggle, his desire to reconnect with his estranged wife, while dealing with the fear of possibly losing her as the terrorist thieves discover more and more about him as he proves to be a proverbial thorn in their side. But better than that, we’re shown a character professionally capable of handling the situation (he’s a cop) but lacking the means to do so (he doesn’t start the movie with a gun or shoes). So, McClain must figure out a way using the infrastructure of the building to take on a great many well armed guards and subvert the terrorist plot. The movie is known for it’s utter willingness to beat the tar out of it’s hero by having him sustain injuries as he attempts to stop his enemies. These injuries are used as a second source of tension in the movie, watch how the running gag about McClain being unable to find a pair of shoes that fit lead to him cutting up his feet on glass scattered across the floor from bullet fire. Then, watch how his enemies use his bloody trail as a means of tracking him, adding yet another layer of tension and worry over whether or not he can succeed. Die Hard is definitely over the top in the same way most action movies are, but it was a reaction against most of the films in the 80s. It’s a great example of how to make a story, even one that is exceedingly over the top, still feel incredibly, nail bitingly, real.
Whether your characters are worrying about snipers on the rooftops in a confined urban environment, trying to identify and shoot targets through a window while trapped on the third story, fighting their way up a staircase, picking up a pen off a desk as a means of self-defense, or transforming someone’s liquor cabinet into an arsenal of Molotov cocktails, it’s important to track how a character deals with their surrounding environment, how that environment affects them, and what part it plays in a fight.
Here’s an example of what I mean:
Quivering in her chair, Leah watched as the man in black approached the desk. She could hear the shouts of her father’s bodyguards outside, yelling for reinforcements. The crack of gunfire snapped through her ears and her teeth rattled, numb in her mouth. Echoing through the open window, the rat-a-tat-tat of controlled bursts filled the courtyard below her father’s office. There were more yells. Then, each familiar voice fell silent.
Her palms pressed against the desk, the green felt scratching at the pad of her right index finger. Sweat left her hands slick as she chewed her lower lip and wide, damp circles darkened on the papers detailing “The Trans-migratory Habits of the Native Red Squirrel”. It was the essay her father had spent the last few month typing up for the Chamber of Controlled Ecosystems. He’d refused to use a computer, she remembered, this document was typewriter only.
“So,” the man in black said as he placed his hands on the edge of the desk. “We meet again.”
Leah stiffened, teeth sinking into her lower lip. “I guess,” she replied, swallowing. Father always said it was important to sound calm. She looked down, eyes darted sideways to the ballpoint pen tucked halfway underneath another pile of papers to her left. Her father loved stout, metal pens. She leaned forward a little, letting her fingers inch towards it. A pen wouldn’t be as good as her father’s letter opener, but the man in black would definitely notice if she went hunting through the drawers. Leah’s eyes closed. “I mean,” she said. Keep your voice steady like Father taught. “I don’t know who you are.”
“No?” He asked.
Leah’s fingers closed around the pen. She looked up at him, meeting his clear, blue eyes. They were sharp and hard like the ice that froze the courtyard pond every winter. The courtyard pond that was probably now filled with red…she sucked in a deep breath, shoulders tensing. He was right, there was something familiar about those eyes.
“No,” she said. He tilted his head. Now or never. Leah shoved herself forward, body shooting across the desk as she seized his wrist. Yanking him towards her, off his feet, as he crashed into the edge, she lifted the pen high into the air. His right arm sent her father’s World Cup mug crashing to the floor. Her thumb pressed down on the top and she slammed it into the back of his exposed hand.
The man in black let out a howl, something caught between a scream and a roar, as he reached towards the wound. She let him go and he stumbled back, grasping the pen. Leah wasn’t going to wait for his response. Bracing her hands under the edge of the desk, she heaved upward and pushed forward. It toppled, much more easily than she’d expected, to the floor. All her father’s work dumped to the ground. Leah turned on the ball of her foot, racing around the desk as the man in black let out another savage cry.
She hit the door, fingers fumbling for the knob.
“You won’t escape from me, Leah!”
Glancing back over her shoulder as she shoved the door open, Leah swallowed. “I can try,” she said. Then, she slid out into the hall and slammed the door shut behind her.
It’s not perfect, but it might give you some ideas.
If you’re stuck on how the military works, it’s important to note that because Army field manuals are published by the U.S. government (Department of Defense/Department of the Army) that they are available to the public for free online as pdfs. This wiki page has the links, they may be helpful to getting a better grasp of military armed conflict.