Dave Worsley: On Novak Djokovic retiring from the Australian Open Semi-Final

A shock withdrawal at the Australian Open for ten-time champion Novak Djokovic. The Serb great sensationally withdrew after losing a marathon first set of his semifinal against second seed Alexander Zverev, in a tiebreak. Meanwhile, the reigning men's champion faces a tricky match-up in his semifinal tonight. LISTEN ABOVE See omnystudio.com/listener for privacy information.