They have it from BFV Firestorm. It's called "Downed But Not Out" and you can enable it for Portal matches.
Once you are downed, you get another 150pts (as BFV firestorm gave you 150 health) that will start depleting, and getting attacked or shot or any damage will make them run out superfast or just kill you officially.
While DBNO, you can use a melee weapon on those that are close enough (standing over you usually) or your sidearm/pistol. But everything is slower and it's a bit out of focus and hard to aim. It's phenomenal.
I hope more enable it on Portal matches because it's such a great addition. You can read about it if you search "Down But Not Out BFV"
