Okay some people have agreed with me and strangely some havent..
I have come across the situation where I have been moving and pushing with my fellow teammates and someone comes out of nowhere and chainsaws you.
Within a second I am chainsawed and the other kid is killed by my buddies shotgun.
You know what I am talking about? When the opposing player doesn't finish the chainsaw animation because he is killed?
I think that if the chainsaw isn't atleast halfway down the body, or if the chainsaw literally touches you for a second and then the opposing player is killed you should be downed (DBNO) considering you technically really didn't get chainsawed. This helps keep the noobs from getting the kill and keeps you alive.