Being a defender, let's say it outright, isn't a position that's sought or loved by many players. Most will prefer the glory of a capture and the big points that come with it. They generally see in defense a boring position, and boy, are they wrong. Any defender reading this will understand. Offense players will never feel the unique thrill of chasing down an enemy flag carrier, Taking back what is yours from his cold, dead hands, neither will they feel the simple joy of doing something that is just as important to victory - if not even more important - as offense.
Unfortunately, it's not all as exciting as chasing down that mother****** who thought he'd look really cool with your team's flag on him. There are several other duties you'll have to assume. Though all of them are tightly related, always, always remember them all.


-Base cleaning:
Simple, and essential. You don't like it when you return the flag and see it gets taken a split-second afterwards huh? Well, guess what, nobody does. That's a good start to begin being useful, and is a recommended choice for new people in CTF. Just try to considerably shorten the life span of anyone entering your base, no matter what. Hunt them down ON SIGHT. Don't wait for them to be able to grab the flag to start worrying, or it will be too late.


-Flag carrier defense:
Every offense player out there will agree with me here: there is no more desolating perspective for an offense player with the enemy team's flag than having to fend off waves and waves of enemies with nobody to give a hand. There are several points you have to keep in mind, but they can all be resumed to this phrase, which must be your mantra: "I can use /kill. He cannot. I am the pawn in a chess game, he is the king".

* Let him have all the ammo he needs or wants. If you run out, /kill and grab your guns again
* Let him take all the health kits and shields he wants. If you get low on health, /kill
* And last but not least: TEAM HEAL / ENERGIZE. SPAM IT. EVERY. F***ING. SECOND. I cannot stress enough the importance of this. Team Heal and energize win games. What do you think that is best, having him, who may need at any moment to speed up to run or fight, and that must not at any instance die, heal 25 HP for 50 force, when you, who can kill yourself and return to the fight with losing nothing more than mere seconds, can heal him by 50 HP for 20 of your force?


-Flag chasing and returning:
You were waiting for this, didn't you?
Allright, the first mistake you should avoid is to automatically run behind the enemy. If you can use a shortcut to intercept him, DO IT! It's by far easier to shoot someone who's running towards you or towards the sides than someone going in the same direction you do. Why is that? Well, at a higher level of play, players are so fast they're likely to be nearly as fast as rockets. I think you can understand why this poses a problem. If you do manage to make it in time, try to position yourself so your victim won't see you until you start firing. I also found dropping from a higher level onto your target helps immensely, for both aiming and for the surprise effect.
This also goes when you aren't at the base when the enemy grabbed the flag: Wait somewhere you know he'll have to go through, such as say, the bridge area in CTF4 (in my own CTF vocabulary this is known as a chokepoint).

Use your force intelligently: you want to be able to keep up with him in case he's got enough for a sudden boost. Pull is your friend, but you must not go overboard. Spamming pull is frowned upon. It is besides a very dumb idea. Why? Because in most cases, a smart offense player will turn on absorb the second he is pulled/pushed for the first time, and any extra pulling will only fill his force pool. Well, not really. In some cases, it can be wise to pull someone who's using absorb, but only once, so as to slow him down. Then, Immediately shoot. He'll be a sitting duck for just that mere fraction of a second. You must, however, be aware of the fact that this is a very risky maneuver, only to be used in extreme cases: Screw up and he'll slip away with the Force you gave him. And this is of course bad, because it is simple logic that a flagger that returned to his own base is, by far, more likely to defend himself effectively than when running away. This leads me to my next point:
ALWAYS, ALWAYS, do your best to return the flag BEFORE it reaches the enemy base. If it does, your task will become WAY harder.
But let's say he does get to his base (we'll assume there is a stalemate). In this case, a rule of thumb is to maintain pressure on the enemy base at all costs. A flagger that's constantly fighting will soon run out of ammo, force and health, AND will NOT be able to blow himself up and grab the flag a second time. Any second you waste while getting back to his base gives him a second to get ready for the next assault. It is also important to consider your priorities. This sounds obvious - Most of, if not all the time, you'll go for the flag carrier until you or him die, but make sure you wipe out teamheal-happy defenders (luckily for you, those are rare) if they become too much of an annoyance. They'll be back in just a few seconds though, so don't miss that chance!

And finally, remember how I stressed the importance of flexibility in CTFs, in my basics article? This of course still applies to all positions, but remember: You might be forced to grab the flag to prevent a capture. If you do, forget about your flag unless you are absolutely sure you won't screw up. Otherwise, get the hell out of there and let someone else do the job.


Hoping this helped,
Uncle Macey.