In the ongoing match between South Africa & West Indies, during the toss, South African captain Temba Bavuma said that wicketkeeper Quinton de Kock has made himself unavailable for the match due to personal reasons. 

The reason being speculated is Quinton de Kock didn't want to take the knee in favour of the 'Black Lives Matter' against racism. Cricket South Africa (CSA) Board on Monday unanimously decided to issue a directive requiring all Proteas players to adopt a consistent and united stance against racism by “taking the knee” prior to the start of their remaining World Cup matches.

As we saw in South Africa's first match against Australia, several players from South Africa didn't take the knee before the match.