Game one of four card players has left (5)
I believe the answer is:
Here is my best explanation:
'game' is the definition.
(I've seen this before)
'one of four card players has left' is the wordplay.
'one of four card players' becomes 's' (bridge players are called N,E,S and W).
'has' is a charade indicator (letters next to each other).
'left' becomes 'port' (left side of a ship - opposite of starboard).
(Other definitions for sport that I've seen before include "entertainment", "Fun; wear", "Games", "Game; display", "Abnormal", "Physical exertion and competition", "Show off", "eg Soccer", "exhibit" and "Physical recreation".)