The game was blown away from Manchester United's reach from the first minute after Erik Ten Hag's back four. The manager started Harry Maguire, Lisandro Martinez, Diogo Dalot, and Luke Shaw at the back. 

This four players are incompatible and they lack communication in the defensive unit. The counter attack that led to the fourth goal was because of the zero rapport between these four players. It was a horrendous performance by the players but the manager is to blame for trusting the wrong players.

2. Trying to play the ball from the back

Ten Hag must have forgotten that this is not the Netherlands, he can't play from the back with vulnerable players like David De Gea, Harry Maguire, and Diogo Dalot. 

The second goal conceded by United was an error from Eriksen, he tried to start the build-up but the ball was intercepted by Brentford players. No one was open to getting the ball from Eriksen, and the manager is failing to see that these players are not getting his pattern of football.