I gotta be honest, I know of no one special way to beat up someone in COD4. From what I understand people have no shared unifying characteristics. They walk and talk and breathe and have dreams just like any people. (Well, maybe not dreams. They are in a game, after all. Only nightmares for them... nightmares that come true every time they open their eyes and see that i'm playing with them) Anyone can choose to play COD4, when beaten down enough by life, as a signal to the world that they've given up. There's nothing about someone in COD4 specifically that lends itself to any one maneuver.
That being said, this seems like a good time to mention an incredible tactic that works on many people I've encountered, including those in COD4. It's called "the dick punch."
The dick punch is an incredibly devastating maneuver that, mysteriously, only works on roughly half the population. It's uncanny, how it seems to play out that way.
For example; a few weeks back I ventured into a fraternity house on a nearby college campus.( college searching ) Stuff got a bit out of hand and so I was forced to start dick-punching people like a dick-punching fiend. Every

le person in there collapsed when struck by the move. Not two nights later, I was at a sorority house on the SAME CAMPUS. SAME TIME of night, SAME SITUATION... and THE DICK PUNCH HAD ABSOLUTELY NO EFFECT ON ANYONE IN THERE. I was mortified. It was like they'd cast a protection spell against it or something! ( WOW noobs )
Unbelievable, right? Trust me, I was there, it happened. Unfortunately, science will never be able to tell us why this is. We just have to accept it.
Step One: While facing your enemy and standing still, quickly bend at the knees, tucking your legs towards your body so that your calves are horizontal to the ground. You'll float there for a moment or two, absolutely still, until gravity kicks in, rapidly pulling you towards the ground.
Step Two: When you feel the wind in your hair, indicating your descent, immediately throw a straight right hand. It will connect solidly on your opponents d-zone, instantly dropping them in a heap.
This move should be practiced many, many times before deployment in an actual fight. Be advised, you'll feel a sensation in your lower body the first time you try the move. That feeling is the pain from both your kneecaps having just shattered. A small price to pay for mastery over the greatest technique in fightdom. Over time, those kneecaps will heal, eventually building up enough resistance to withstand the impact.
The timing must be perfect. Be careful not to throw the right hand, and then drop, as the positions will be off and you'll harmlessly punch your opponent in the chest or rib area. If you punch too late, after having already hit the ground, your foe will have probably caught on and will likely knee you in your face-part. It must be one

le fluid maneuver: bend knees, hover, drop, then punch.
Yeah, it's a beautiful move...
If I had a nickel everytime the d-punch bailed me out of a fight... I'd have zero dollars. (I donate all my frequency-of-events-happening money to orphans... aka my "future army" ) However, before I gave it away, I will say it seemed like there was quite a lot of money there. ( like a truck load of dimes!! the suspension on my truck is still in shock )
Remember earlier when I said there was no specific tactic that applied only to COD4 noobs? I lied. Suddenly running up behind a person in game, while screaming loudly, and then boxing their ears as they turn towards you WILL INSTANTLY DISABLE ANY PERSON in game. Then, use the dick punch to finish them off. As the "state of noobing" ranks just behind the "state of nausea" in a list of things to be avoided, take no mercy on these miserable fucks.Also a very hidden secret is still in development. code named "kick" and an even more regrettable fate codenamed "BAN".
Now remember your service to the world and start fucking up those noobs!