John Cena appeared on SmackDown in Chicago one last time, and he confirmed a rumor that has been circulating in recent days. Not only this, but he was also confronted by a top champion in a full-circle moment, one that had been a decade in the making.Chicago gave John Cena a beautiful reaction when he appeared in their city for his final appearance as an active performer. He reminded them of the significance the city and building have, as it was where he made his debut, first headlined WrestleMania, had iconic US Title open challenges, and came in second place to CM Punk (at Money in the Bank 2011). In doing so, he confirmed the rumor that September 5 would be his last-ever SmackDown appearance.Not only this, but as he was saying his goodbye, he was interrupted by the newly-crowned United States Champion, Sami Zayn, in a full-circle moment from 2015. Sami Zayn asked to carry on the tradition of the US Open Challenge, and he said that he wanted to face Cena first. So, what is the context of this full-circle moment after Cena accepted the challenge?Back in the post-WrestleMania 31 season in 2015, John Cena was in Montreal for a United States Open Challenge, in the early stages of an iconic run. Bret Hart came out and introduced the hometown boy, Sami Zayn, and as an excited Zayn was entering the ring, he threw his arms up and busted his shoulder.He still continued the match anyway, but did so in pain, and this kept him out of action for several months. It was an unfortunate moment that derailed his career for a short time, as it was rumored that he was set for a main roster call-up. Kevin Owens took that spot instead, and thankfully, things worked out as they were meant to.