I think this picture best sums up what's wrong with our defense.
Firstly , Dier is standing infront of everyone , clearly highlighting a lack of communication between him and the rest of the back 4 , we need a leader in there not players playing by themselves on their own instincts.
Next , Where is Serge Aurier? Oh yeah that's right he's nowhere to be seen because he doesn't even play as a RB effectively. Consequently Lo Celso/Sissoko have dropped into the 4 you can see infront of Dier , what does that mean? It means 4 Sheffield United players are left on the edge of the box where Lo Celso/Sissoko should be , if one of them had been there Berge wouldn't have been able to pick up the ball and consequently score.
I've always said we needed a CDM but I feel like any player that plays in that midfield will always be dragged out to the right to cover for Aurier , we cannot continue to play like this where our team is so lob-sided and players are filling in for Aurier half the game. The first thing we have to do is buy an actual RB.
The squad currently has 1 natural RB and 1 Natural LB , that's honestly not good enough.
A lot of these defenders are poor and have regressed but having a CDM and midfield that does it job tracking back all the time , would certainly make the team more solid.
If I was incharge I'd look for a NEW CB , RB , LB and CDM.