When Mike Sabin sees someone knocked out or stumbling around the footy field, he likens the feeling to "having butterflies with wings of barbed wire zooming about in my stomach".
He believes it is a post-traumatic stress reaction: it is the same he experienced on Anzac Day, 2009, when he was told his son Darryl would likely die after suffering a catastrophic brain injury.
Worse, Mike had seen it coming, but was powerless to prevent it.
Mike knew with "every cell in my being" that Darryl was on a collision course with something terrible.
Darryl's teenage rugby career had been littered with concussions and he was forced to sit out the end of the 2006 season after successive blows.
In his first game back in 2007, Darryl took another blow to the head, was unconscious for 40 minutes and spent six days in hospital recovering from a bleed on the brain.
In the hope of convincing him to give up for good, Mike took Darryl to a neurologist. He expected medical opinion to support his belief that his son should retire.
"The neuro consultant told Darryl [the issue] had resolved and healed and there was nothing to suggest [it] would happen again, which obviously caused me a fair bit of alarm," Sabin says.
"I said, 'Well, Doc, look at what's happened over the last 18 months. Just about every game he plays he takes a dong on the nut that most people would walk away from, and if you look at the incidents, each one is getting progressively worse'. He just reiterated the fact that there is nothing medically to suggest that would happen."
Through a mixture of pleading with his son and getting the coaches behind him, Mike managed to keep Darryl off the field until 2009. By then Darryl had moved to the Far North to work on a farm and his father learned he was taking up rugby again.
"I just felt sick. The whole script was unravelling," Sabin says. "The doctors may have said there is nothing to suggest it would happen again, but every cell in my being was telling me it would."
He spoke to the Northland Rugby Union to see if there was anything they could do to de-register players deemed to be medically at risk, but there was no provision for that, so he began looking into a court injunction.
Sabin never got a chance to see whether he had a valid platform - he was on the phone to a lawyer talking through his options when a police car pulled into his driveway and the butterflies with wings of barbed wire descended.
Rugby may have nearly taken Darryl's life, but it's also helping to bring him back from the dead.
"Rugby has been the cornerstone of his recovery - ironic I know," Sabin says.
Darryl had suffered a massive bleed on the brain and was not expected to survive. If he did, the family were told he would be in a vegetative state.
As Darryl battled for his life in Auckland hospital, then-All Blacks coach Graham Henry was visiting his brother-in-law in the room next door, and after learning of the teenager's horrific accident, slipped a note under Darryl's pillow, wishing him well.
According to Sabin, the family "was hours away" from making the call to turn off his life support when Darryl wiggled his left thumb to let "us know he was in there".
That was the start of his remarkable recovery, as over the next year he had to re-learn how to see, eat, speak and walk again.
Inspired by his battle, the All Blacks named Darryl as their official 23rd man and he can be seen sitting on the reserves bench most games.
He has drunk from the Bledisloe Cup, the Tri Nations Cup and the Rugby World Cup and boasts all sorts of All Blacks' memorabilia, but most precious is the note he received from his special mate Ted.
Rugby and brain injuries
Monday: Paul Tito's career ends; and the spectre haunting contact sports
Tuesday: Nicky Allen's brother accuses NZRU of "laundering" issue; and Stuart East's sleepless life
Wednesday: League's tardy reponse; and Dean Lonergan's fit relived.
Tell us your story
If you have had problems with concussions received playing sport contact us at firstname.lastname@example.org.