That must be it. Walker was the toughest nut in the AFL till Carl started scripting Neil Craig's press conferences.....
We've seen on a couple of occasions that Walker's first instinct was to bump rather than tackle. Technically this is a bad move, but it is inherently aggressive. The coach has been pushing the message that he doesnt believe in toughness and won't tolerate players being reported, leads to the player second guessing their natural instinct.