* Trainer Battle: This is the most common reason. The screen flash is a visual cue that signifies the start of a battle. It's a dramatic way to transition from the overworld to the battle screen.
* Wild Pokémon Encounter: Similar to trainer battles, wild Pokémon encounters also feature a screen flash to indicate the battle is starting. This helps you know you're about to fight a Pokémon.
* Special Battle Effects: Some battles have special effects that can cause screen flashes. For example, certain Pokémon abilities or moves might trigger a flash.
* Graphics Glitches: Rarely, a screen flash could indicate a minor graphical glitch. This is less common but can happen in older Pokémon games.
To determine the specific reason, pay attention to:
* Who you're fighting: If you're facing a Trainer, it's a normal battle start.
* What's happening around you: Are you in a specific location or encountering a certain type of Pokémon?
* Any unusual visual effects: Is the flash accompanied by other visual effects like a specific sound or a change in the environment?
By observing these factors, you can usually pinpoint the reason for the screen flash.