Scared of getting injured again. He does not and will not commit to the tackle any more and shies away from being tackled by dropping to the floor at the first chance!
However... he said he wanted out, was told he had to complete his contract, then threw his toys out of the pram and committed his contractual breaches for which he was sacked. Therefore the root cause was then he wanted to leave, he just went about it in an unprofessional fashion.