Backdoor

Backdooring (abbr. BD) is the commonly used term for a strategy, often as a last-resort against heavy enemy pushback, where one or more team members will attempt to attack the enemy team's base structures forcefully and/or end the game by destroying the Nexus, without the support of allied pushed minion waves. In other words, backdooring means sneaking into the enemy base without having pushed the lane first.

Strategy

The benefit of this strategy lies in the element of surprise. For example, an ally may jump into and threaten the enemy base by going through the jungle, while the rest of the ally team distracts or otherwise pressures the opposing team to make a quick decision during a major objective such as Baron Nashor and Dragon (which are far away from the base) and/or prevents enemy recalls. Players have the opportunity to notice when a lane is being pushed alongside minion waves and may thus potentially move to defend it before the enemy reaches a structure; backdooring on the other hand, especially if enemy lacks vision in the path that the backdooring allies have taken, can allow a team to rush structures before the defending team has a chance to react. Mechanics that give champions higher chances and a way easier time of sneaking into the opposing base include:

• Being able to jump over the enemy base's wall (e.g. Talon's Assassin's Path, Shen's Shadow Dash)
• Speed into the base with exceptionally high movespeed (e.g. Sion's Unstoppable Onslaught, Udyr's Blazing Stampede)
• Have access to camouflage in order to avoid ward detection (e.g. Akshan's Going Rogue, Twitch's Ambush)
• A global or near-global teleport (e.g. Teleport on an undetected ward, Twisted Fate's Destiny, Pantheon's Grand Starfall)
• As well as have access to enormous structure rushdown damage (e.g. Veigar at high amounts of AP late-game, Neeko's Shapesplitter's passive, Rengar's Savagery, etc.)

Structures are unaffected by critical strikes,  life steal,  armor penetration, and many on-hit effects. Therefore, generally the highest risk-reward strategy on any player aiming to backdoor is to sell certain items and invest on the best combination of stats and effects available from items that specifically increase the efficiency of taking down structures, namely  attack damage,  ability power,  attack speed and Spellblade items.

Counter-strategy

If a team suspects that their enemy may attempt a backdoor, they may leave one or more champions to ambush the attackers, as being alone deep within the enemy's territory can prove to be very dangerous, especially if the champions have no escape abilities. A teammate spotting the attackers and their allies reacting fast enough to the noticed attempt, may also instantly end that attempt at backdooring if the attacker cannot move past the defense safely and/or in time to finish the backdoor successfully.

Wards and especially Control Wards against camouflaged champions and potential enemy Teleport targets may be placed at possible infiltration points and/or inside the base, in order to potentially notice enemies attempting to backdoor earlier and before significant damage has been done.

Turrets also have Reinforced Armor protection, which heavily reduces incoming damage from enemy champions when there are no enemy minions nearby. This is a mechanic specifically designed to render backdooring turrets more difficult. Inhibitors and the Nexus do not have this protection, meaning they are fully exposed to champion damage.

Reception

Backdooring is considered unsportsmanlike by some players and is especially frowned upon by casual players. Some players actively "ban" the strategy when playing their own custom games. The majority of competitive players, however, accept backdooring as being a legitimate strategy.

The strategy is also not punishable in any way in casual or competitive and professional games.

Trivia

• The term "backdooring" was originally coined by RTS players of games such as Warcraft and Age of Empires.
• By contrast, "frontdoor" can refer to directly rushing down a structure visibly against the enemies, although this usage is almost never seen in MOBA games anymore. In addition, this has been proven to be almost impossible in modern League of Legends. However, tanky rushdown champions in the late-game such as Nasus, Dr. Mundo, and Yorick may still rarely and under the right circumstances, achieve a successful "frontdoor".
• During IEM Katowice Season VII, xPeke, a member of team Fnatic at the time, backdoored the nexus against SK Gaming. The play can be viewed here. Due to the exceptionally difficult and exceptionally risky nature of using such strategies in professional play, xPeke's successful backdoor has been noted as one of the highest and most iconic achievements in professional League of Legends.
  • Veteran players may still refer to backdooring in general as "pulling (= performing) an xPeke".