Even in the 30 or so steps leading up to the tackle my mind had time to run through the moral implications. I could have pulled back but my teammates started cheering me on. We'd talked about this rule change in training. The opposition clearly hadn't.
Their team was too stunned to warn the halfback until far too late. The howls of outrage from their supporters on the sideline, the look of pure disgust from the mothers had no time to register.
Woefully unprepared for the hit, their halfback went down hard and had to be assisted off the field.
But we turned the ball over and won the scrum. Job done.
Rugby is a violent game. That's probably why it is game of choice for much of the business world.
Those perennial debates about the relative skill of football (ie soccer) versus rugby miss the point. It's true that only the goal kickers on a rugby field can claim the kind of technical dexterity that rivals the best football players. But rugby is part martial art. It has as much in common with boxing as other ball sports.
At its heart, what separates good from great players is mental discipline. It is about using maximum force without stepping over the line by breaking the rules or - worse - seeing red and forgetting to think.
Great players draw on the adrenaline that flows from a body convinced it is at war, all the while maintaining the presence of mind to contextualise the game around them.
It's a huge mental challenge. We expect players to be as mean as the rules permit, and perhaps a fraction meaner as long as they don't get caught, but we also expect them to remain calm.
There are historical and cultural reasons for the game's rugged yet elite reputation.
Rugby, so the saying goes, is a thug's game played by gentlemen. Football is a gentleman's game played by thugs.
It is a definition heavy with the implications of the English class structure.
Football evolved from the medieval streets; rugby has its roots in the elite public school system.
There's Rugby school itself, but also on the fields of Eton, Harrow et al, the game once played an important role in hardening up of well-to-do British boys.
It prepared them for the officer class and for making the kind of cold-hearted decisions needed to maintain an empire ... or a business.
That culture spread through the Empire and further. The game maintains an elite cultural position in places like Argentina and even the USA. Rugby is the only competitive, extramural team sport offered at Harvard Business School.
New Zealand if anything has led the way in bringing rugby to the masses. Its adoption by Maori and its uptake through all levels of colonial society is special to this country.
But even so, New Zealand business has the stamp of rugby all over it.
Our greatest business success is the dairy industry. It was forged by hard-nosed business people, many of whom forged their mental toughness on the rugby field.
That era culminated with rugby fanatic Craig Norgate who was instrumental in uniting the tribes and creating Fonterra.
It is widely accepted that Wilson Whineray is one of the greatest All Black captains but he is not nearly so well recognised by the public as one of the nation's most successful business leaders - which he was.
David Kirk and others have followed in his footsteps to the upper tier of the business world. Ironically, though, the professional era with its big money and media careers may have killed the phenomenon.
Business and rugby have simple aims: Make money, get the ball across the line. But both are rendered infinitely complex by rules which narrow the options for achieving these aims.
Staying focused on the basics while negotiating a minefield of complex and often inane rules is crucial in both fields.
New Zealand rugby fans love to label teams like the French and Springboks dirty but really that's just part of the fun. You'll seldom hear the All Blacks complaining. Those who play the game know it is not cheating until the referee tells you it is.
The difference between an accidental knee in the head and deliberate one can be as subtle as the divide between tax evasion and tax avoidance.
So, here it is - time at last for the Rugby World Cup. Let's win it. In all its brutal, ethically ambiguous glory, let the rugby begin.
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