The one thing that Riot hates is bugs especially the ones that require it to disable even one of their champions for a few hours. What about a bug, that caused anyone in ranked matches to be has instantaneous recall? Well, that is exactly the kind of bug that Riot has had to deal with leading them to disable all ranked matches and there still does not seem to be a proper fix in place.
The bug was first discovered on the champion Riven, but later it was discovered to affect all champions and players leading to some very interesting issues such as this video where Skarner could use the bug to instantly kill a champion.
When working recall is supposed to allow a champion to return to their base after a few seconds of standing there. While it is being channeled you are unable to do anything else.
Riot normally addresses small issues by disabling a particular champion or item however, this issue was more widespread and game breaking then what was originally thought which has caused Riot to disable ranked matches for several hours now and there has been few updates regarding it. The most recent one shows that they have manged to solve the issue for some select champions and are going to finish the testing phase.