While fans are still divided about whether The Legend of Korra was a worthy sequel to Avatar: The Last Airbender, it's undeniable that the former expanded on the Avatar universe masterfully. Legend of Korra contained several callbacks to the original series, but one especially subtle reference was the sport of Pro-bending. Its similarities to the Earth Rumble 6 tournament Toph Beifong used to participate in are unmistakable.
During Aang's search for an earthbending teacher, he was directed to Earth Rumble 6 as the place to find the strongest earthbenders within the Earth Kingdom. The sport was easy enough to understand -- earthbenders battled it out in no-holds-barred matches where competitors were free to use any earthbending techniques at their disposal. Victory was only achieved by knocking the opponent out of the ring.
Even back then in Last Airbender, the loosest structure of the sport that would become Pro-bending in Legend of Korra was visible. Of course, new rules were added since The Blind Bandit last graced the ring. Earth Rumble 6's "anything goes" battles put both the competitors and spectators at risk.
Pro-bending fixed this issue by providing standardized disks that the earthbenders could fight with. Attacks aimed at opponents' heads also attracted penalties, but the strategies either team could attack with were virtually unrestricted. The game's main objective was also unchanged; victory was achieved by knocking an opponent out of the ring.
Earth Rumble 6 might have never evolved into what Avatar fans recognize as Pro-bending had the United Republic never been created. Before the end of the hundred-year war, benders of specific elements were concentrated in their respective home nations. It was only after Avatar Aang formed the Republic and its capital city that the Avatar world's rich cultures had a chance to mix. Benders and non-benders from different nations intermarried and shared their traditions, beliefs and the games they enjoyed.
As the United Republic was carved out of Earth Kingdom territory, its natives were already familiar with tournaments similar to Earth Rumble 6. The unbridled violence must have appealed to non-earthbenders eager to prove their mettle and the sudden influx of new bending styles to a beloved sport definitely wouldn't hurt viewership at all. Judging by how popular Pro-bending had become in Korra's time, the demand must have been high. After centuries of watching solo earthbenders, who wouldn't want to watch teams of diverse benders?
The Last Airbender's Earth Rumble 6 must have had to go through several reinventions before emerging as Pro-bending, but certain traditions still remain. For example, The Legend of Korra's unnamed announcer had a personality almost as big as Shin Fu's. Interestingly, Pro-bending's public perception seems to be a lot more positive than Rumble 6's.
While Rumble 6 matches were more of an underground affair, Pro-bending is openly celebrated in Republic City. The finals in Book 1 of The Legend of Korra were a significant enough event that Amon's threat became the subject of a council meeting. Notable companies lined up to support the participating teams, and the benders themselves were quite well respected.
