When going up against hordes of the Ridden, some teammates will inevitably go down and need a revive in Back 4 Blood. But the revival system in the game is relatively straightforward.
Going down in Back 4 Blood is simply part of the game when too much damage is taken, and with four players running around the area, revivals are important. If the situation arises and a player goes down, the teammate that needs a revive still has a chance to provide some damage. They will be given a secondary weapon to continue shooting the Ridden as they are on the ground.
How to fully revive a player who has died in Back 4 Blood
Players can run over to their downed teammates and hold the interact button on any platform. It will take a short sequence to fully revive the teammate, so it can be dangerous if there are too many enemies in the area. If the players don't revive their teammate in time, the timer will wind down and the downed teammate will die.
In cases where there is simply no chance of getting revived, downed players can hold the button to die and skip past the timer. While it will mean death in Back 4 Blood, that's not the end of that chapter. Players who die will spawn away, and a new objective will be given.
As mentioned, after a downed player runs out of time or bleeds out, they are dead. But instead of being stuck watching their teammates, they will be transported to a new part of the map where they respawn.
However, the process isn't that simple, and players can't simply walk back to their teammates after they have respawned. Instead, they will be stuck in a slime-like substance, and teammates will need to get them out.
Typically, the respawn won't be too far away from where the player died after going down, but it essentially becomes a new objective. Once the rest of the team finds the trapped player, they can remove the slime and give a full revive within Back 4 Blood.
From there, the full squad of Cleaners can continue down the chapter area in Back 4 Blood. Hopefully, players in the game won't need to complete the full process often, and the normal revive can be enough.