According to Business Insider, "James Harden set NBA Twitter ablaze on Tuesday night with a behind-the-back sidestep move that many believed to be traveling.
The NBA referees association explained why the move was legal." The NBA referees association tweeted, "The point of contention seems to be what is consider the "gather-step," at which point the player dribbling gathers the ball and puts a foot down almost in the same instant. In this case, the NBA is ruling that the gather-step takes place as Harden moves the ball behind his back and establishes his right foot as the initial pivot."