San Francisco 49ers quarterback Colin Kaepernick stands on the field before their NFL pre-season football game against the Denver Broncos in San Francisco, California, U.S. August 8, 2013. REUTERS/Stephen Lam/File Photo

Cycling - Tour de France cycling race - Stage 18 from Sallanches to Megeve, France - 21/07/2016 - Movistar Team rider Nairo Quintana of Colombia cycles during the individual time trial. REUTERS/Jacques Clawey

Ariya Jutanugarn (THA) of Thailand watches her tee shot on the 14th hole during second round women's Olympic golf competition. REUTERS/Kevin Lamarque

Britain Tennis - Wimbledon - All England Lawn Tennis & Croquet Club, Wimbledon, England - 2/7/16 Serbia's Novak Djokovic celebrates during his match against USA's Sam Querrey REUTERS/Stefan Wermuth

Germany Formula One - F1 - German Grand Prix 2016 - Hockenheimring, Germany - 29/7/16 - Red Bull Racing's Max Verstappen attends the practice. REUTERS/Ralph Orlowski

Germany Formula One - F1 - German Grand Prix 2016 - Hockenheimring, Germany - 31/7/16 - Red Bull Racing's Max Verstappen during the race. REUTERS/Ralph Orlowski

Germany Formula One - F1 - German Grand Prix 2016 - Hockenheimring, Germany - 31/7/16 - Mercedes' Nico Rosberg during the race. REUTERS/Ralph Orlowski/Files

2016 Rio Olympics - Tennis - Final - Women's Singles Bronze Medal Match - Olympic Tennis Centre - Rio de Janeiro, Brazil - 13/08/2016. Petra Kvitova (CZE) of Czech Republic celebrates after winning match against Madison Keys (USA) of USA. REUTERS/Toby Melville