Ok here's a pretty over-simplified analysis of our defensive issues:
Do not mark an opponent until screamed at: Murphy, Browne (joke's not lost on me

)
Regularly fob off opponent to a defender when they push too far into the defensive 50: Simpson
Tendency to over-commit to 'secondary' defensive play: Yarran, Wiggins, Walker, Russell, Johnson
By the last category, I refer to committing to a chase down, a zone-off, bump or gang-tackle without a real consideration of what options your opponent(s) have, or a half-decent plan in mind as to how to affect the play. Essentially: game-sense.
Yarran is somewhat excused as a first year player who is recognised as a natural attacking type. Browne gets a down-graded spray but should know the basics.
Murphy: riot act. I want him walking away from Ratten too scared to wipe off the 100 mL of spittle he receives during the bake. Undid all his good work of the past 4 games in the last two rounds. Simpson should get a spray and correct his issue quickly, always has.
Russell made very few mistakes beyond the kick-outs, and his portion of the blame is rather minor when you think about that. But he did have a concentration lapse in marking his opponent that cost a goal.
Walker spent the first two and half quarters steadily getting better with the ball but wound up being almost useless without it. By the end of the game he was ok, but the pressure was completely off. Really needs to focus on not lairising around when marking an opponent; regularly ineffective when leaping in as the third, sometimes fourth, man.
Wiggins & Johnson fit into the opposite category as Walker: started well and slid away. Same zone-off/third man issues and Johnson in particularly smashed in as the second tackler on one occasion as the ball was coming loose, went to ground and watched as an Adelaide player scooped up the ball (play was at about the 50 arc) and slotted a goal.
Immensely inconsistent from guys that should be regarded as senior players. One minute they'll be standing goal-side of their opponent, then they'll still be goal-side but two metres off their men, soon to be scratching their heads as to why such a ploy backfired. Then on another occasion, they'll be well forward of their men or half-way into a hole, then slow down as they back track to a better position: why?!