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However, a team like Man United taking such a defensive approach is strange. Its unusual for a club with their history and ambition. It casts doubt on their strategy and league standing.
I think Ten Haag was more focused on not getting more embarrassed so I didn't find it unusual to be honest. You can notice how United cannot really find a good mix of offense and defense. They can score if they open up but they are also prone for allowing many goals and we've seen that a lot in their previous CL matches this season. The same thing could have happened against Liverpool if Ten Haag decided a more offensive approach.
Yes you are right, man utd was very cautious with their approach to the game, the 7-0 lose the last time is still fresh in the back of their minds, so to me it quite logical that they took such approach due to their defensive frailties this season.
If they had come out toe too toe with Liverpool they would have scored a goal, but they would have lost whole fully.