Blaming Maguire is a bit silly, he can't mark everyone.
In reality, we have a goalkeeper who likes to stick to his goal line, and very few dominant aerial players in defence, never mind the rest of the team. I don't think our planning is great, either. Just yesterday I noticed Fred marking Michael Keane, for instance.
Exactly. There is plenty of blame to go around.
We have Fred, Shaw, and AWB as man markers, starting around penalty spot. Our better headers are on 6 yard line, maybe to protect De Gea and to attack the ball.
In theory they should be able to attack the ball and be moving away from our goal as they do that.
In reality (because DeGea can't command balls into 6 yard box) the ball is coming on top of them. These guys are are static, while the opposition (DCL, Keane, Mina, Otemendi) get a running start.
Who is to blame?
Ole/coaches for the set up.
De Gea for being poor commanding his area.
Fred, Shaw, AWB for not impeding the runners, they can't be expected to actually compete when they are so outmatched physically. But yesterday they gave them a free run.
Maguire, Lindelof, McT for not attacking the ball coming into their zones. But they are at severe disadvantage due to reasons above.
The amount of issues means blame has to go to sideline.
Another potential issue could be our defenders practice against the likes of Lingard, Martial, and Rashford every day, which isn't exactly testing them aerially.