Board Thread:Boruto Discussions/@comment-28432164-20160514001744/@comment-26127155-20160514222125

Guys this is a new manga and we do not know how far in the future the Boruto Vs Kawaki fight is set. for all we know a surprise back stab (similar to Madara and black zetsu) could have happened to Naruto, and Kawaki is just rubbing it in to Boruto.

About Naruto being rusty, it has been shown that most Kage (and other leaders like Hanzo) don't have the time to train and keep their skills sharp. Naruto might not have had to fight for years at a time which would definitely affect his fighting abilities. Hashirama and Madara were only able to keep their abilities honed for so long, because they lived in a time where combat was apart of everyday life. Hashirama's death itself could have been due to how he probably didn't fight much after he defeated Madara, and when he went into the 1st Ninja war, he got his ass kicked for lacking the sharpness that he previously had.

I'd like to think of that like if you told one of the best sports stars to not play a game or train for their sport for a few years, they are going to be a shell of themselves coming back into action.