UEFA published a report explaining why the referee did not disallow Ajax’s third goal against Real Madrid even though the ball appeared to be out of bounds when the play was escalating.
Real Madrid CF – AFC Ajax
Ball in/out of play - 62’
There was no conclusive evidence that the ball would have been entirely out of play from all video angles and images that were carefully analysed by the VAR.
The assistant referee, who was perfectly positioned, had adjudged that the whole ball had not fully crossed the touchline. No on-field review was therefore required. Consequently, the referee was right not to intervene and to allow the goal.
This goal probably decided the tie and it would have been great to have the proper technology to determine whether the ball really stayed in the field of play or not. Given that the initial call was to let the play develop, the replay showed no evidence to overturn the call and ultimately disallow Ajax’s goal. In the end, the right call was made.