#2 The playing surface
There was some conversation about the actual playing field affecting the game ahead of AZ Alkmaar's home clash with Manchester United as they played out 90 minutes on an artificial grass pitch. The visitors appeared to be struggling with the pace of the game in the beginning and improved considerably towards the end.
On plenty of occasions we saw the ball skipping away from Angel Gomes and Daniel James as it tended to skid off the surface, especially when played over longer distances. It was another area where United had to adapt and by the time they were starting to look slightly more dangerous, it was perhaps too late.
Alkmaar did plenty tactically to stop Manchester United from attacking effectively, but they also benefitted from the fact that Manchester United had to adapt to playing conditions that they aren't entirely familiar with.