Sure, here's an example of a simple gun fight game implemented as a single HTML file, using JavaScript and enclosed in script tags:
This game sets up a basic gun fight scenario where the player can move left and right using the arrow keys on their smartphone screen. They can also shoot bullets by pressing the space bar. The game loop continuously updates the game state, and the health bar is displayed at the top left corner of the canvas. Feel free to further customize and add more features to this game as desired.