Jack Sock is an early contender for 2016's most sporting act. 

The American tennis player was facing Lleyton Hewitt in the Hopman Cup when he told his opponent to challenge an incorrect call by the umpire. 

"That was in if you want to challenge it", Sock shouted across the court to his be bemused opponent. Hewitt obliged and challenged and luckily for the American player, his original thoughts were correct. The ball was indeed in.

His good sportsmanship failed to win him the game though. Hewitt won in straight sets.