NEW YORK : World Athletics has added the indoor 4x400 metres mixed relay to the rule book as an official discipline, the sport's global governing body said on Wednesday, ahead of its indoor championships debut next year. A crowd favourite thanks to its unpredictable nature, the outdoor version of the event made its Olympic debut in Tokyo four years ago and since then has produced some memorable moments for the sport. Organisers will hope to replicate that popularity in the indoor format as the