Before we get too far into talking about defense, I wanted to talk a bit about the goals for the Summoner's Guidebook. My goal is not to elevate people to the ranks of the top players, as there are many websites already dedicated to that. The Summoner's Guidebook is specifically targeted at less-experienced players who do not already know the ins and outs of the game. Inevitably, this will result in topics that are fairly well-explored by advanced players.
The goal of the Guidebook is to broaden the horizons of players who don't yet know all the tricks and strategies. While I do link to other articles or videos to illustrate my points, the Guidebook is intended as a standalone resource for players trying to learn the game. It is hard learning to play LoL as a newbie. League of Legends is a very difficult game to learn, especially if you learn on Summoners' Rift. While no amount of reading can replace practice, the goal of the Guidebook is to lessen that burden and illuminate some of the more arcane elements of the game.
This inevitably means that higher-level players will not find everything here useful. Hopefully, it is still entertaining to read, but being entertaining is not my goal. My goal is to teach, and the people in the greatest need of learning are novices. Once you're an expert, I highly recommend going to LolPro or SoloMid.net; they are fantastic resources and helped me personally improve my game.
And now, back to your regularly scheduled program!
Defense multiplies just like offense
Although it is commonly thought that defense follows diminishing returns, that is not exactly the case. Both armor and magic resistance follow the same basic rule: Each point of armor/MR that you get gives you 1% effective health against that particular type of damage. If you have 100 armor, you have 200% effective health against physical damage. If you have 150 MR, you have 150% effective health against magic damage.
Armor and magic resist also increase the effective value of shields and heals. A 200-point shield is effectively 300 extra hit points if you have 50 armor. Heals and lifesteal effects also are effectively multiplied; healing yourself for 50 HP means 150 effective health against magic damage if you have 200 MR. If you're a champion like Udyr, Warwick, or Mordekaiser, raising armor and magic resist give you a much greater benefit than raising maximum health. Additionally, the value of lifesteal multiplies if you also have defense. Consider this if you have a Bloodthirster. Extra defense helps make that lifesteal much more significant in terms of long-term survivability in a fight.
Extra HP is almost always good, too. If you already have a lot of armor or magic resist, bonus health becomes very good. Getting 200 extra HP means a lot more if your Rammus has 400 armor and 250 MR.
Damage resistance also exists, though it is much rarer. The main way to itemize it is from the Dominion-exclusive Odyn's Veil, which gives 10% resistance to all magic damage. Some champions, such as Poppy, Olaf, and Alistar, also have resistance abilities. Combining these effects with Odyn's Veil does not have an additive effect. Percentage resistance multiplies on all other forms of resistance and also multiplies on itself. Kassadin's passive and an Odyn's Veil multiply to reduce incoming magic damage on him to 76.5% rather than 75% as expected.
Practical use of defense
One of the earliest uses of defense is to avoid being detonated by a burst caster. In the midgame, many casters have an incredibly powerful combo that will take off 70-100% of your health bar if it strikes you. Mercury Treads will soften the blow, often reducing death combos down to a more managable 50% of your life bar. A Negatron Cloak and the items that it builds into can also nullify the threat altogether. Even if you're focusing on building up your damage, you can grab items like Hexdrinker or Wit's End. If the enemy has a roaming burst caster or you're on Dominion against someone like Akali or Kassadin, you cannot neglect magic resist or you will pay the price.
Defense is what makes dueling possible. While damage is always a plus in a 1v1 or other small engagement, defense cuts down a lot of enemy damage for an exceedingly low cost. Acquiring 45 armor or MR costs roughly 700 gold, and that's an extra 45% effective health. It costs over twice that much to deal extra damage to counter it, and this can lead to victories in 1v1 even if your opponent is slightly ahead. Additionally, many defensive items have fantastic dueling benefits, such as the attack speed slows of Randuin's Omen or Frozen Heart.
One of the simplest counters to an enemy autoattack champion is Thornmail, which does a large amount of reflected magic damage back at the enemy. Many AD champions build more lifesteal to counter Thornmail, but this is a colossal mistake -- they're making the fight go faster but usually not in their favor. If the enemy builds Thornmail (or is Rammus), get magic resist! Because the reflected damage is magical, MR can shut down a lot of it. Here's an example: I was playing bottom lane in Dominion, and the enemy Tryndamere came down to fight me in the late game. He was pretty fed, and he could easily defeat me in a 1v1 confrontation. However, I spent some of my surplus cash on a Thornmail and easily crushed him afterward, despite his having multiple lifesteal items, using his ultimate, and starting the fight with full rage. MR can help you avoid being in the same situation as him.
Later in the game, enemy damage is through the roof. An enemy AD carry can typically three-shot an opponent with no defense (sometimes even two-shot), so building some armor in the lategame is mandatory unless you fight from so far away that there is no risk at all of being hit.
Diminshing returns again?
Although defensive stats always give a consistent amount of effective hit points, there is a somewhat diminishing effect on the value of defense. If you already have 200 armor, building more armor will not give you as much of a benefit as building damage. Additionally, having a huge number of tank items will discourage the enemy team from attacking you, which encourages you to build damage since you will not be focus-fired.
At lower skill levels, this is less true. Opponents frequently focus the easiest available target, which can lead to strong advantages with items like Thornmail. In general, if you are frequently the last ally standing in a fight as a tank, you could probably benefit from more damage items.
Some characters also have amazing base values that work just fine without needing extra damage items. Maokai, for instance, deals reasonable damage even if he is built as a full tank. However, most tanks will want to build something to solidify themselves as a threat. Typically, this is simply an item like Rod of Ages, Trinity Force, and Atma's Impaler, which synergize well with tanky builds. You should look at a build guide for the specific champion in question. While general advice is helpful, it will not replace specific knowledge of your character.
When to buy tank
It is usually a bad idea to buy defensive items right away, as damage is more important for last-hitting and winning your lane. Damage is better if you are poking a lot and worse if you are getting in a lot of sustained engagements. If both you and your opponent are poking but you are coming out behind, the answer is usually to play better and not to build defense.
If you are in a kill lane (a lane where one side is focused on getting kills), it is probably still better to build damage early rather than defense. If the enemy opponents are well-suited to killing their lane opponents rather than farming, the answer is to play safely and deny those opportunities rather than try to fight your way out of them.
I find myself wanting to build tank roughly around the time that my opponents reach the 5000-gold mark in the early midgame. At this point, the enemy generally has upgraded boots, a completed high-damage item, and several additional items that also boost damage. This is the first time when you should consider buying tanky items, but you can probably delay them if you are decisively winning your lane. If the situation is fairly even and you want to get ahead, tanky items can provide a boost when you commit to an engagement. However, if you have a strong jungler, you may still want to focus on damage to bolster the effectiveness of his ganks.
I do believe that building tank items after the 10k-gold mark is probably a little late. I find that at that point, enemies are doing so much damage that any mistake results in an empty health bar. While the answer can be to simply play more safely, tanky items provide a bit of a buffer and also allow you to bait an initiation more effectively.
On the Crystal Scar, tank items should be built sooner. Because teamfights occur as soon as the game starts, building any defense is helpful as the enemy will damage you unless you don't engage at all. The exact time to start is very champion-specific, but in general, building more tank helps you engage earlier and longer. If you're built as a glass cannon, you must frequently delay engaging until much of the fight has already occurred and your contribution will often be less than a more hybrid approach. Additionally, base numbers on skills are frequently more meaningful to the outcome of a fight than damage built from items. If your champion is focused on autoattacks, damage is always going to be mandatory, though.
While tank is a very important thing to build, and knowing how it impacts the game is critical, the exact timing of when to build tank is more art than science. When it's done just right, you truncate most of the benefits of your opponent's big ticket items. When it's done poorly, you end up contributing little due to mediocre damage. As with all things, there is no substitute for practice. Good luck and have fun!
We understand what it's like to climb the skill ladder in League of Legends. The Summoner's Guidebook teaches you the tools you need to get a competitive edge. Whether you're climbing the ranked ladder, playing Draft Dominion, or getting crushed by intermediate bots, every enemy has a weakness. And every Thursday, Patrick Mackey shows how you can improve improve on yours.