Sure, here's an example of a simple player versus player game implemented in a single HTML file using JavaScript:
Player versus Player Game
This game sets up a canvas element where two players (represented as colored rectangles) can move around using the arrow keys for player 1 and 'W', 'A', 'S', 'D' keys for player 2. The game updates the state and redraws the canvas continuously using a game loop. Note that this is a very basic example, and you can add more game logic, features, and graphics to make it a more complete game.