As an AI language model, I can provide you with a simple example of a football game implemented as a single HTML file using JavaScript. Please note that for a complete and complex game, additional libraries, assets, and game logic would be required. Here's a basic example to get you started:
This example sets up a basic HTML file with a canvas element and initializes the ball position and speed. The `updateCanvas` function clears the canvas, updates the ball position based on its speed, checks for collision with canvas boundaries, and renders the ball on the canvas using the `arc` method. The game loop is achieved using `requestAnimationFrame`, which continuously calls the `updateCanvas` function for smooth animation.
Please note that this is a very simplistic example and can be further extended with additional game logic, controls, scoring, player interactions, etc.