Sure! Here's an example of a simple shooter game implemented as a single HTML file, using JavaScript and enclosed in script tags:
In this game, the player (represented by a blue rectangle) can be controlled by touch-based inputs on a smartphone. The player is moved horizontally based on the user's touch position on the screen. There is also a bullet (represented by a red rectangle) that moves upwards. The bullet position is updated on each frame, and when it goes off the canvas, it is reset to the player's position.