If we've made him play on when clearly concussed then we deserve to be bent over a barrell.
If it was negligence in not noticing he was concussed when assessing him then it's not as bad, but still crap by whoever did the assessment (it's not unheard of for players to say they're fine, it's up to the medic to see through it).
This was pre HIA, wasn't it? So it was someone who would have gone on to the pitch to check him?
I'm not sure that failing to notice a concussion is quite so forgivable. If this happened, surely the club failed in their duty of care for their employee.
I'm not sure how relevant HIA is here, this is a UK law matter, not one of rugby rules / regulations, although the court may well take queues from the recommendations of the governing bodies at the time. As the protocols in place at the time were very poor, I'd have thought that Willis' lawyers would be arguing medical malpractice rather than failure to follow guidelines. As has been noted, I'd have thought that any physician would testify that a player's own opinion of their ability to carry on playing safely is close to irrelevant - they're not medically trained and may have recently been subject to brain trauma, making it a weak defence against malpractice.
I would have thought that the process of establishing culpability is as follows:
For starters, you would need to establish that this incident lead to his being forced to retire.
If it did, did the medical practitioner fail to make a competent assessment of the injury? If not, no case to answer.
If so, then was the practitioner sufficiently qualified? If not, then the club have failed in their duty of care, so must be liable.
If so, then it sounds like medical malpractice, so all that's left to establish is whether the club are vicariously liable for their employee's incompetence or whether the liability would lay with said practitioner (and his / her insurer).
One more thing that I'm surprised hasn't been noted, if Willis is related to BOD, presumably, he's related to BOD's uncle Barry, who has been outspoken about World Rugby's handling of concussion. I wouldn't be at all surprised if it's him behind the scenes pulling the strings here.
FWIW, I'm glad to see a case like this brought. It's unfortunate for Sale that they're on the receiving end and I accept that at the top end of the game, concussion is being taken far more seriously and being dealt with better, but it's a useful reminder to all clubs, particularly those further down the pyramid of the potential consequences of not taking this seriously.