Warzone Rumble is a new mode in Warzone Season 4.
If you've paid attention to the battle royale scene for the past few years, you'll see the similarities between the mode and the 50-vs-50 in Fortnite which was introduced earlier on in the game's history. It gives players a break from the typical battle royale mode while still having the ability to to farm attachments and unlock weapons in the game.
Warzone Rumble Introduced in Season 4 Update
Much like the Fortnite version, players will continue to fight until the enemy team runs out of respawns, and then the team is wiped out. So players will be able to respawn and enjoy the battle until the resources are complete, then you'll have just one life left.
The more tactical and patient the team is, the better chance at success. Do your best not to waste your team's revives.
Activision and Infinity Ward also enabled multiplayer for free during Season 4's launch weekend.