Basically what the title says, a loss should be prevented when you join into a game and you’re placed into the losing team especially with Warzone and BTB. For example, in Call of Duty Black Ops 3, the match that you join in progress and you lost the match, your loss wouldn’t be counted in your statistics.
At least you’re getting replacement players on your team. I’ve lost track of the number of times I’ve ended up in a BTB match where half my team quit and it was 4 v 8. The game wouldn’t find us replacement players, and there was no mercy rule despite the enemy team being up by 60 points. And you can’t quit either otherwise you’ll be penalized for leaving.