Physical violence and fighting can be a wonderful source of conflict in fiction … when it’s done well. A fight should tell a story that’s integral to the overall narrative, and the tone of the action should not feel out of place.
Most violence and martial arts portrayed in fiction is filled with various levels of fantasy, even in otherwise realistic stories. There’s not necessarily anything wrong with that, but frequently I think writers are attempting one thing and doing another.
When writing a fight scene it’s important to understand the kind of fight you want to write. You can imagine your fight existing somewhere on a graph with realism vs. fantasy on the x-axis and serving the story vs. the inconvenient truth on the y-axis. Great scenes can be written anywhere on the graph, but it helps to know where you are and what you’re up against.
In this context, realism is an adherence to the laws of physics and the demonstrated behavior and abilities of real people. Fantasy may break these rules, but should have a set of internal rules the characters and actions adhere to.
Serving the story is the necessity of certain actions or outcomes for the sake of the overall narrative. The inconvenient truth is everywhere the rules of realism or the internal rules of fantasy are in conflict with those actions and outcomes. Sometimes it’s okay to break the rules, but go too far and readers will be put off.
Martial arts and fighting are rich fields touching upon physics, culture, technology, anatomy, phychology, history, and human ability. It pays to do some research! As with most things, the more knowledge and experience you have, and the clearer your objectives, the more confident and convincing your fiction will be.