"man down" = a phrase to use in battle which means that a soldier in your group is lying on the ground. This has been twisted into Caribbean slang to signify the same thing in context but with literal meaning and sometimes physical. Usually as an answer or response to a situation where a person doesn’t overcome the obstacle in it’s path. Example: Guy1: What did you get for the test ? Guy2:*Hand Gesture* MAN DOWN! Scene: A gang of dudes chilling outside talking when somebody happens to fall in a humorous but serious manner, Someone yells: MAN DOWN! Source: www.urbandictionary.com

man down = a person has been hurt or incapacitated in some way but NOT dead yet (often a team or group member)

It's a military term. It means that someone has been injured in battle. It can mean killed but not always. And it's usually yelled out or screamed.

for my own opinion it means someone get hurt. cowboy...

I think it usually means someone's been killed.. :(