#8 Sting was supposed to return as a mystery partner at SummerSlam 2015
At WrestleMania 31, Sting lost his WWE debut match in a wildly entertaining brawl against Triple H, only to shake his hand out of respect moments later. It was not the ideal way for Sting's WWE career to begin as his first ever appearance in WWE at Survivor Series 2014 was amazing. However, the plans for his summer would have been far better-received than his role at 'Mania. The original plans for SummerSlam would have seen a six-man tag team match pitting a reunited Wyatt Family, Bray Wyatt along with Luke Harper and Erick Rowan, taking on Roman Reigns, Dean Ambrose and a mystery partner.
The partner would have been Sting, but those plans went out the window when Rowan suffered an arm injury at the end of June and the match was pared down to Wyatt and Harper vs. Reigns and Ambrose instead. Braun Strowman was considered to make his debut in Rowan's place, but it would have been overshadowed by Sting's appearance. In the end, Strowman made a surprise debut the night after SummerSlam, while Sting re-established his presence on the same night as he targetted WWE World Heavyweight Champion Seth Rollins. Sting would eventually retire after suffering a neck injury during the ensuing match against Rollins at Night Of Champions.
#7 There hasn't been an entirely clean US title match since the 2005 edition
It is quite astonishing to believe, but the last clean United States Championship match at SummerSlam happened thirteen years ago, in 2005. Chris Benoit took 22 seconds to beat Orlando Jordan to capture the US Title, becoming the last person to win a clean match for the star-spangled belt at SummerSlam. From 2006 to 2014, we did not have a single US Title match on the SummerSlam main card. Santino Marella lost the belt to Cesaro at the 2012 show, but that was the pre-show. This changed, quite aptly, when SummerSlam arrived at Brooklyn.
In 2015, Seth Rollins defeated John Cena in a title-for-title match to win the United States Championship, while retaining his WWE World Heavyweight Championship. However, the match ended when SummerSlam host Jon Stewart interfered and hit Cena with a chair. The following year, Rusev's scheduled title defence against Roman Reigns was cancelled when the two brawled endlessly at ringside. Last year, we saw Shane McMahon officiate the US Title match between AJ Styles and Kevin Owens in a match where he was heavily involved, especially physically. Unless you insist on counting that match as a clean one, the last US Title match at SummerSlam that was entirely clean was in 2005, and it lasted 22 seconds.
#6 Randy Orton was John Cena's backup for his match with Seth Rollins in 2015
Four weeks before the aforementioned title-for-title match at SummerSlam 2015, John Cena defeated Seth Rollins in a match on Raw where only Cena's US title was on the line. This would build to their match at SummerSlam, but we saw a pretty gruesome occurrence during the match. Rollins hit Cena right in the face with a flying knee which looked absolutely brutal. Cena's nose was left completely battered and misshapen, casting a serious doubt over whether the Cenation Leader would be cleared for the pay-per-view.
The backup plan if Cena couldn't work SummerSlam was to take Randy Orton, who faced Sheamus in the show-opener and have him face Rollins instead. The two did have a match for the World Title on Raw in the build-up to the summertime spectacular, but Cena would indeed be cleared on the week of the show. He wrestled with a torn tricep at SummerSlam two years earlier, so it was pretty safe to say that a broken nose was not going to hold him back either.