Riot Games has temporarily disabled ranked matchmaking for League of Legends.
They have taken this action as a consequence of a bug affecting the Recall ability. Recall, like using a hearthstone in World of Warcraft, allows the player to teleport back to base. Recall is not risk free; if you don’t choose you path carefully, there’s a risk you’ll be hurt along the way.
So what does the bug do? It makes Recall work instantaneously. The bug was originally observed on Riven, so she was temporarily disabled. However, as more characters exhibited the bug, Riot eventually chose to just turn off ranked mode.
Riot shared these status updates regarding the situation:
We're currently working to fix a bug with the Recall spell. Unfortunately, this particular issue can't be mitigated by disabling a specific champion or item so we've temporarily disabled Ranked while we develop a solution. We will update you all with our progress in 12 hours. (9:08 AM, Network Operations)
We're still working on the fix that will allow us to turn on ranked queues in all territories. We completed the code change and are currently working with our Quality Assurance testers to verify this issue is fixed. We will update the status soon with more news. (9:53 PM, Riot Eglorian)
For the moment, players have normal mode to play with, but since the bug is still being investigated, using it comes at your risk.