Sure! Here's a simple shooting game implemented as a single HTML file using JavaScript and enclosed in script tags:
In this game, you control a blue player square using the arrow keys on your smartphone. Pressing the spacebar shoots red bullets from the player. Green enemies move down from the top of the screen, and your goal is to shoot them before they reach the bottom.
Note: This game is a simple implementation and can be enhanced with additional features, levels, and graphics as desired.