During the June 2019 Pokemon Direct, a number of brand new concepts coming to the World of Pokemon were revealed for Pokemon Sword & Shield. One of these concepts is called Max Raid Battles. These types of battles correspond with the concept of Dynamax. Max Raid Battles appear randomly in the Wild Areas across The Galar Region, and they are a multiplayer feature that see trainers trying to defeat a Wild Dynmaxed Pokemon.
This Wild Dynamaxed Pokemon, however, does not revert to normal after three turns. Up to four players can challenge a Max Raid battle, connecting either locally or online. (If you can't do either, you will play with NPCs Support Characters.) During Max Raid Battles, only one player can Dynamax a Pokemon. Each player can only bring one Pokemon into a Max Battle with them. Furthermore, a protection barrier will appear midway through a Max Raid, one that must be destroyed before the Wild Dynamaxed Pokemon can be hurt once again.
After defeating the Wild Dynamaxed Pokemon, players will gain the ability to capture it. Wild Dynamax Pokemon change every single day and vary based on the location they are found in the game and the Weather of that given area.