Sure, here's an example of a simple billiards game implemented as a single HTML file using JavaScript:
In this simple billiards game, a red ball is bouncing around inside a canvas element. The ball's position and velocity are updated continuously, and its motion is handled by reversing the velocity whenever it reaches the edges of the canvas.
Note that this is a very basic example and doesn't include any gameplay mechanics specific to billiards. You can further enhance the game by adding game logic, such as player input for controlling the angle and power of the ball, collision detection between balls, and scoring mechanisms.
To run the game, simply copy the code above and save it as a ".html" file. Open the file in a web browser, and you should be able to play the game on your smartphone by interacting with the canvas element.