Croatia has played in the extra time of each of their first 3 knockout stage games in the 2018 World Cup. They played Denmark, Russia, and England in the round of 16, quarterfinals and the semifinals respectively.
What is the most number of games a team has played extra time in a single World Cup? Similarly what's the most number of consecutive extra time games played in a single World Cup?
Before the start of FIFA World Cup 2018, 63 previous matches have gone to extra-times. And after manually checking this FIFA document (contains record for matches up-to 2006 world cup), 2010 FIFA World Cup results and 2014 FIFA World Cup results:
Most number of games a team has played extra time in a single World Cup is 3 times and 3 teams have done it so far England 1990, Argentina 2014 and Croatia 2018.
Most number of consecutive extra time games played in a single World Cup is again 3 and 2 teams England 1990 and Croatia 2018 have obtained this feat.
Reference: Live Match-blog England vs Croatia FIFA official site
Interesting fact: Croatia are the first team to come from behind in three straight knockout stage matches to advance at the World Cup.
