I've previously thought he's been a bit suspect at Centre Back however, something is not working at the back currently.
We've tried a three and a four and honestly they both look bad for different reasons. The personnel at full back have actually improved from last season, JG back and Thompson in clearly is a step up. William's has basically been swapped for Casey at CB with the other personnel staying the same there. Whilst RW really hasn't been great it doesn't completely explain the defensive drop off a cliff, realistically it's what's happening in front of them.
Under Quitch everything was in front of them, we generally had at least parity in possession if not controlled it which played perfectly into not very fast but thinking defenders Marvin, Thorniely, Husband etc. So for me the play and personnel in the middle of the pitch is killing the defensive line. Now, the midfield is so porous the opposition can range passes and runs in behind our back line seemingly at will through out the game, which is a complete nightmare for Marv, Rhys, Thorneily and Husband if he were to come in ( he does seem to have a decent turn of pace as compared to the others but I don't think that style of play will do his body any favours). I'm not sure a simple swap out of players sorts this.
Realistically the players we have at centre back need the ball controlled in front of them, with any break down happening well in advance of them allowing them to drop deep under no pressure and do what they do best. The midfield is, and has been a mess for a long time, we all know about the impotency it creates up top but with out Quitch's style of ball possession it is now really damaging the defensive players.
We need a sea change at central midfield, ideally we needed an Ellis Simms or similar to be signed this summer just gone to operate as a loan striker and load the midfield with five players. However we have a collective of strikers that are extremely limited at this level of football.
With what we actually have at the club, I think we need a four in midfield Connelly alongside Patino in the centre with Lavery on the left as he's neither use nor ornament as a striker, but his tenacity shone through in the role he played during the Burnley seond half, maybe Poveda on the right, need to see more of him. I'd try Jerry and Theo as a pairing up top and ban long balls to either of them.
The playing staff has not yet caught up to Appleton's style and might take another 12 months to do so, as I've said before this might be an ugly season.