Sure, here's an example of a simple billiards game implemented in a single HTML file:
This billiards game features a red ball bouncing around the canvas and a blue paddle at the bottom that the player can control using the arrow keys. The objective is to prevent the ball from hitting the bottom wall by deflecting it with the paddle. If the ball touches the bottom wall, a "Game Over" message is displayed, and the game can be restarted by reloading the page.