As an AI language model, I can help you with an implementation idea for a simplified text-based version of "Rocket League" as a single HTML file with JavaScript code. Please note that the code provided is a basic example and may not fully replicate the gameplay experience of the actual "Rocket League" game. Use this as a starting point and expand upon it to create a more elaborate game.
This simple game involves two players, the player and the opponent. The goal is to simulate scoring goals in a match by calling the `playMatch()` function. The scores are displayed using the `displayScores()` function, and there's also a button to reset the scores.
Please note that this is just a basic representation of the game mechanics. For a more realistic and interactive experience, you would need to implement more functionalities like player movement, ball physics, input handling, and graphics.