Sure! Here's an example of a simple football game implemented as a single HTML file using JavaScript:
In this game, the football field is represented by a green box, the ball is a white circle, and there are two blue players at the bottom.
You can control the players using the arrow keys (left and right) for player 1, and the 'a' and 'd' keys for player 2. They can move horizontally within the field. The ball is fixed in the center initially, but you can add logic to move it around the field based on player interaction.
Note: This is just a basic example to get you started. You can enhance the gameplay further based on your requirements.