This weekend, the new tournament mode Clash should have started in League of Legends. However, due to technical issues, the event had to be canceled. In addition, the LoL mode ARURF, the 2018 replacement for URF, is available.
After the successful beta test, the new team-based competitive tournament mode Clash was supposed to debut this weekend in League of Legends. According to Riot, the opening weekend was a failure due to technical problems, which is why All Random Ultra Rapid Fire, short ARURF, is being played now.

Riot wonderfully honest
Technical issues despite beta: In mid-December, the beta for the new tournament mode Clash took place. This mode was intended to be held several times a month and allow players to compete in teams against equal opponents in brackets with a knockout system.
The new tournament was designed for five-player groups and also introduced special rewards that can only be obtained in this specific mode.
Event canceled: Shortly after the start of Clash, the event had to be canceled again this weekend. The cause was critical technical problems that affected not only the European version but also the international version of the game.
Riot itself labeled the introductory weekend of Clash as a “failure,” which is why the popular mode All Random Ultra Rapid Fire, short ARURF, is now being played. As the developers did not have much time to test the mode with the current patch, there could be bugs or strange interactions in ARURF. Therefore, it may be that Riot has to disable some champions or runes.
This is what the players say: Many players are disappointed and blame Riot – for example, under the official statement from Riot on the American website. The company has allegedly overhyped the new Clash mode unnecessarily over the last six months, only to cancel it at launch due to difficulties.
Some players had already planned this weekend for a long time and are now disappointed. Riot apologized and announced that they are working hard to ensure that the mode can take place soon. The tickets used for participation in this event will be refunded.
No URF – only ARURF in League of Legends
URF is not returning: The original mode URF, Ultra Rapid Fire, seems not to be returning to League of Legends. According to the developers, URF led players to not want to play LoL anymore.

In this mode, abilities cost no resources and the cooldowns were reduced by 80 percent. Additionally, the movement speed of all champions was increased and gold was earned quickly, allowing for faster item purchases.
All of this led to some champions becoming overpowered. As a replacement, ARURF was introduced, where players are assigned champions randomly.