Sure! Here's a simple example of a 3D running game implemented as a single HTML file using JavaScript. It uses three.js library for 3D rendering, and the game can be played on a smartphone:
This game is a simple infinite runner where the player has to jump over obstacles. You can control the player by pressing the space or up arrow key to jump. The game starts when you press Enter or touch the screen. The score increases as the player progresses, and the speed gradually increases over time.
Please note that this is just a basic implementation to give you an idea of how a 3D running game could be built. You can customize and enhance it further based on your specific requirements and visual design preferences.