A croquet player on Court 2 at Cheltenham Croquet Club.
To play a croquet stroke, the player needs to hit one of the other balls with the ball they are playing. The ball that they played is then picked up and placed in contact with the ball that was hit. The ball in play is then struck in such a way that both balls move - this is the 'croquet' stroke.
There are various types of croquet stroke - this gentleman is playing a 'stop shot', where he has struck the black ball so that both it and the blue ball with which it was in contact are both moving: the outcome of a 'stop shot' is that the 'forward' ball (ie the blue) should move a much greater distance then the back ball (ie the black). In this instance the player needs the blue ball to travel toward one of the hoops near the corner of the court, but needs the black ball to end up close to the yellow ball for his next stroke.