They have done so through an explanatory video on Twitter, where they show that a tiny part of the ball was still within the limits of the pitch when the cross that led to the goal was made.
The much-spoken-about controversy arose in the match between Spain and Japan when Japan's Kaoru Mitoma crossed the ball after it had already seemed to have visibly passed the byline. His cross led to Ao Tanaka's goal which was to be the winner as Japan held on for a famous 2-1 victory.
The goal was initially ruled out and then allowed after a VAR review.
Much of the controversy was surrounding the images, or lack thereof, available on TV broadcasts during and immediately after the match.
FIFA has taken almost 24 hours to explain the decision. They have confirmed that the circumference of the ball, not the base, was still slightly hovering above the byline as contact was made for the critical cross.
See FIFA's explanatory video below.
