Shingo Kunieda, who retired last year from his legendary wheelchair tennis playing career, has embarked on a new journey as a coach in the United States in a bid to make his sport as big as it possibly can be. In January, Kunieda traveled to America to develop junior athletes on an invitation from the United States Tennis Association in his hopes that a wheelchair tennis boom there could invigorate the sport around the world. “If America starts producing one top player after another, there is a chance it will lift the entire sport. I want to create that transformation,” Kunieda said recently. …