Only knifing is the weakest tactic in the game. All you have to do is grab a tactical knife and just run around with Commando Pro, Marathon Pro and Lightweight Pro.
Requires absolutely no skill other than jamming the melee button every time you see a player and running around like a tool.
I seriously wish they took out the tactical knife. It just totally forgets over gameplay, here you got sniping and shooting on front lines and stuff then its all flipped tits up because some stuffball is running around with a tactical knife.