For players, to be able to receive Clan Wars rewards, their clan must be placed on one of the rewarded positions (usually it's from 1 to 3) Only those players who managed to score points in Clan Wars can receive the event rewards.
In Clan Wars events there are tasks in which several players can score points. In such tasks, only a couple of the best scores are being taken into consideration. It may happen that a player scores some points in such a task but after that, other players will score more points than him which will result in a player being removed from the task ranking. In such cases, the player score in this task will be set to zero.