Yeah, I was really pissed off a few times because I just didn't make sense. I even tried to knife one guy but then he turned around and knifed me in the face. I was like (

) and then tried to figure it out knowing there was something amiss I wasn't seeing. Then, I tried to knife a guy from the side and he was too busy shooting in the front to realize I'd slashed him 3 times cutting his health down by 60%. Then he just turns and finished me off quickly from full health. Man I was like what the forking hell? Are you serious. Then a little bit later I was thinking I needed to adjust my weapons to fight people to do more damage or something. So I changed my Sprint specialization to Flak so that I could run and gun with damage reduction on my part. Within 10 minutes some guy ran up to knife me.. and I did him the same way with a knife to the face. He died. So.. as far as I can clearly see that is immediately one of the reasons you cannot kill someone in the face or apparently from the side with a knife if they have the Flak on. As Headshot would say, "Their wearing ARMOR I tell 'ya!" In this case it would appear to be true; however, the knife to the back will get anyone and net you a pair of dog tags (which is still cool I think). Also, Flak has it's pros and cons as do all of the other specializations you choose. You run slower I think with it on and give up better uses like extra ammo etc. That's a topic we need to discuss.. but in some areas where the running and gunning is pretty tight I think it makes sense to have it on. Whereas in other areas.. not so much even at the risk of being knifed. Normally I get knifed from behind anyway.. but is it worth it?? the defense I mean.