Lets go through the hierarchy of control:
(snip)
Elimination- would mean stop playing rugby league. Not reasonably practicable.
Substitution- use tackling bags instead of real players. Not reasonably practicable.
Isolation- not practicable in a contact sport.
Engineering- this is things like putting guards on machines, not human movement or other education courses, which would come under administrative controls. Perhaps achieving a high level of physical strength and fitness is an engineering control but it offers little or no control against an injury like this. The state of the ground, its grass cover and consistency underfoot would be another engineering control (knee and ankle injuries are more likely on sandy surfaces)but once again offers no control over risk of this kind of injury.
Administrative- this is where the action is, the only place in fact. It includes the rules of the game and their enforcement, training courses, the judiciary, suspensions, penalties, the sin bin, and so on. This is pretty much the only kind of control the game has for injuries of the type Alex McKinnon suffered, in my opinion. Had the game done enough at the time of this injury to reduce the risk of spinal injuries from dangerous throw tackles to as low as reasonably practicable? That is for a court to determine.
PPE- Helmets, padding, etc. None of which is used in Rugby League. The closest thing to PPE is probably footy boots, which protect the feet. Players could wear suits of armor but it still probably wouldn't prevent an injury like this and it would make the game a completely different and inferior spectacle. Hence not reasonably practicable.