A Rollback is the reversion of in-game content to an earlier state. Rollbacks within RuneScape are used under very strict and rare circumstances. They are generally used to eradicate a problem that cannot be corrected by conventional methods, or as a different punishment for using macro/botting software for the skill botted to level 1.
Player Rollbacking
As stated by JMod Aug, "We, current[sic], do not do rollbacks on request. We only reserve the rollback as a alternative to being permanently banned. When we do a rollback we roll the character back to like they are when they were first created." However, in the past, it was possible. In answer to the question of there being the ability to request rollbacks in the future, it was stated that "There may be, that's all I can say."
Cases of Rollbacks
15 July 2007- Server Breakdown
On this day, every player was unable to log into RuneScape, and every player in every world still in the game were forced out of the game without warning, regardless of any activity. Many thousands of players were online at this time. All accounts which were online at the time were rolled back until the last time they logged in. Many people had claimed to lose expensive PvP loot such as Dragonfire shields and Abyssal whips.
14 April 2010 - The Daemonheim Nature Rune Bug
A bug while Runecrafting within Daemonheim, granted 2,000 experience per Nature Rune crafted, and as Rune Essence within Daemonheim is stacked, this led to many players reaching level 99 Runecrafting within half an hour of the glitch being discovered. This forced Jagex to shut RuneScape down for approximately 4 hours during which time, they made a rollback of player data before the glitch. This led to huge rants on the Forums, players spamming the official sticky article reaching over 3 - 4 pages per second. Forum Moderators stated people were being banned for this, and due to the sheer volume of the spammers, many accounts were likely to have been punished for this. There was no update timer for this rollback, everyone was just forced out of the game without warning.
30 June 2010 - Server Breakdown
Similar to what happened in 2007, many players were not able to log in for more than an hour because of a server breakdown. Anyone who tried to log on received the message "Your account has not been logged out from its previous session." Those who were on (few players) when this happened were automatically logged out and were rolled back. Many of the players logged in at this time, have commented on the "Increased number of Random Events" to any of the players, with statistics showing that 1 in 3 players received a random event before the server breakdown.
23 December 2011 - Server Breakdown
Similar to what occurred in 2010, on this day, every player was unable to log into RuneScape, and every player in every world online at the time was forced out of the game without warning, regardless of any activity. Many thousands of players were logged in at this time. All accounts which were online were rolled back until the last time they logged in.
1 July 2012 - Server Breakdown
Once more, a server blackout occurred, one which lasted for a couple of hours. All accounts which were online were rolled back until the last time they had logged in.
3 July 2013 - Server Breakdown
There was another server blackout, followed by a 20 minute rollback to all players online during the outage.
18 March 2014 - Server Breakdown
A server maintenance breakdown was commenced for approximately 4 to 6 hours with several users being prompted with the message of their account not logging out from their last session. However, those that were in the game stayed in-game without being forced to log out (as opposed to previous cases) until the time they had no choice but to do so. Interestingly, certain users were able to log in without noticeable problems. After approximately 6 hours of maintenance, servers were opened and a rollback was performed with users online during the maintenance losing their progress.
Effects of rollbacks
In the event of a rollback, any experience gained within that that time is lost, as well as monster drops, or even clue scroll rewards. If you received a clue scroll before the rollback period, you will still have that clue, but you will most likely receive a different reward than before. About 10 minutes before the rollback, any player logged in will receive a message telling them there will be a system update, along with a timer next to it. At the end of that timer, the player will be forced out of the game, regardless of location or activity.