Sure, here's an example of a simple game called "Fruit.io" implemented as a single HTML file using JavaScript and enclosed in script tags:
To play the game, copy the above code into a new HTML file and open it in a web browser. The game canvas will be displayed, and you can control the blue player circle using your smartphone's touchscreen. The objective of the game is to eat the green fruits to increase your score and size, while avoiding the red enemies. Every 5 points, you will level up and a new enemy will be added to the game. The player's size will increase by 2% whenever they eat a fruit. The game will end if the player collides with an enemy.