Remember Lawrence Taylor? There are players in the NFL who'll never forget him, opponents who freely admit they spent the weeks leading up to matches against Taylor's New York Giants in a state of absolute fear.
"Something would come over you and you'd just start sweating," Jerry Sisemore, a former tackle with the Philadelphia Eagles, told the 'New York Times'. "My last year in the league, opening day, he immediately got past me ... He just looked at me and laughed. Right there I thought I had to get out of this game."
The game he was getting out of was changing. And Taylor was the man leading the revolution. Prior to his arrival at the Giants in 1981, no statistics were kept to record how often a quarterback got sacked in any particular game. Nor was the positional term, blindside, used. Instead, as Michael Lewis articulated wonderfully in his book, open 'The Blindside', the phrase entered the American football lexicon on the back of Taylor's prowess.
"After Taylor joined the team, the Giants went from the second worst defence in the NFL to the third best," Lewis wrote. "The year before his debut they gave up 425 points; his first year they gave up 257 points. They had been one of the weakest teams in the NFL and were now, overnight, a contender."
And all because of this guy who played left tackle, Lawrence Taylor. "He changed the game," his coach Bill Parcells said. "Until then, the quarterback was every team's key player. But think about it, a quarterback can't keep being the key player if some guy is coming in on his blindside and kicking his butt."
So let's fast forward 20 years to another continent and another sport.
We're in the first decade of a new Millennium and New Zealand - the proudest rugby nation in the world - are excitedly watching the arrival of two new superstars Dan Carter and Richie McCaw.
In Carter, the All-Blacks had an extravagantly gifted out-half, whose capacity to run a game was matched by the physical attributes he'd been born with. Technically, he seemed flawless - either in the delivery of his passes or the manner in which he could glide effortlessly beyond the reach of defenders.
If his team was under pressure, his kicking game reached levels of excellence that few other out-halves in the world could match and whenever New Zealand went on the attack - which, during Carter's career, was fairly often - he had the skill-set to get their backline moving.
The possessor of so much natural talent - all Carter ever needed was the ball.
Enter Mr Richie McCaw Esquire.
If Taylor changed the way coaches and players thought about the role of the left tackle in NFL, then McCaw altered the thinking of rugby people when it came to the importance of a flanker.
"A quarterback can't keep being the key player if some guy is coming in to kick his butt." Nor can an out-half direct the traffic in an international rugby arena if he is on the receiving end of slow - or indeed, no - ball.
But with his career coinciding with McCaw's, Carter rarely had this problem, because in the history of the game, there has probably never been anyone better at forcing turnovers at the breakdown than McCaw, whose technical excellence was matched by an ability to identify an opportunity to steal possession.
The last time I faced McCaw - at Croke Park in 2008 - he wasn't as effective as normal, largely because we focused so much on stopping his threat that we possibly neglected some of New Zealand's other stars. McCaw was quiet but New Zealand still won.
And they have been winning ever since, largely - but not solely - because of their dominance at the breakdown. In attack, their speed at recycling possession is matched by the skill they have in slowing down their opponents' ball when they are defending.
And, as with other sports, when one team is successful, others look at what they do and try to emulate them. As a result, the importance of the breakdown, and by extension, a team's back-row, is valued much more so in the modern-day game than it would have been two decades ago when I was making my baby steps in senior rugby.
Call it the Lawrence Taylor factor - or in rugby terms, the McCaw factor.
All of which brings me to this Friday.
I can't put things in any simpler terms than this. If Ireland win the battle at the breakdown against Wales in Cardiff then they will win the game.
And if they beat Wales, then I believe the momentum they will gain from that victory will sustain them through the following week until they meet England. Victory there will probably lead to a third Championship in four years.
In other words, the battle between the two sets of back-row forwards this Friday is of monumental importance.
And it will be fascinating to watch because this area has been a strength of Ireland's - as it was for Leinster when Joe Schmidt was coaching there.
Then, as they were winning back-to-back Heineken Cups in 2011 and 2012, they attacked the breakdown area with an urgency and an aggression.
Schmidt placed an emphasis on technique, on cleaning out rucks, on figuring out ways of getting opposing players out of harm's way. And Leinster, accordingly, became known as a team who recycled the ball quickly, who built phase after phase of attack, and who left their opponents physically and mentally exhausted.
Prior to then, in 2006 and 2008, we at Munster also viewed this area as one of our big strengths. Rugby is a physical game. Win the collisions and you are halfway there to winning the match.
So we worked on our technique, spent a lot of time thinking about our body height when we entered the contact zone, on presenting clean ball for our scrum-half, on getting opposing players out of the way.
All the time we observed how New Zealand - particularly McCaw - were doing things and we sought to impersonate them. Schmidt, though, took things to an even higher level with Leinster, and again with Ireland.
One of the things the Ireland coach really focuses on is accountability. He stresses the importance of a ball-carrier's technique being top-class, so that he does not flop to the ground after being tackled, but fights to turn his body back towards his team, so that he can supply clean ball.
One thing that is noticeable under Schmidt is that you rarely see an Irish player running in an upright position towards two opposing defenders, because they know if they do so, there is a chance the opposition will have the opportunity to force a turnover or hold him up.
So today's player thinks a lot more about body height than guys from a previous generation would have.
They'll be coached and encouraged to improve their footwork whenever they make a carry, to generate speed, to possibly deliver an offload if they are in a one-on-one scenario, to fight on the ground for every inch.
Schmidt, like every international coach, views the breakdown as a hugely important facet of the game - as McCaw did during his stellar career.
And this Friday we will see six - and if subs are introduced - eight very good impersonators of McCaw.
All eight are superb talents but stylistically very different. The Welsh, essentially, have thus far selected two No 7s in their back-row - and by going down this policy, they have lost a little in terms of a lineout option and grunt - but gained something in terms of the speed, aggression and footballing ability that Sam Warburton and Justin Tipuric provide. Their other back-row options, Ross Moriarty and Taulupe Faletau, are also top-class.
By contrast, Ireland - in the view of some commentators - have two No 6s in their side, although in my eyes, Seán O'Brien is more of a six-and-a-half, a brilliant player at locking onto opposition ball and forcing turnovers, as well as being a man with an unbelievable competitive edge. Complementing him are CJ Stander and Jamie Heaslip - two fabulous players - with Peter O'Mahony a superb back-up to hold in reserve. Accordingly, this area will be a massive part of Friday's game, because whichever side protects their own possession in this sector, while slowing down the opposition ball, can go a long way to winning the match. Back-rows change games.
Think about how Wales beat Ireland in the 2011 World Cup, how New Zealand - with McCaw at his best - beat South Africa in the 2015 World Cup semi-final, how New Zealand thumped the Lions in 2005.
Or better yet, think how Ireland beat New Zealand in Chicago, by applying massive pressure on the All Blacks players at every ruck, by getting all their players, wingers, centres, props, as well as their flankers and No 8 to attack the breakdown. They went into the combat zone that day with the intention of winning that battle. And so they won the war.
Who'll win this Friday? For me, it's Ireland. Wales are good in that department. But Stander, Heaslip and O'Brien may have the edge.
Jamie Heaslip 8
Superb all-rounder, whose reading of the game is outstanding. He is also so competitive at the breakdown and at turning ball over
CJ Stander 9
Has unbelievable power but it is noticeable that his skills have improved, too. So, for that matter, has his work at the breakdown in terms of his technique and body height. His consistency in performance should not go unnoticed
Peter O'Mahony 8
Brilliant at the breakdown, aggressive and a good ball-carrier.
Seán O'Brien 8
Has power, ball-carrying ability, physical strength and when he carries the ball into contact, his body height is really impressive. So is his speed on the ground, which helps to force turnovers. Injuries have hampered him
Sam Warburton 8
One of the best in the world at the breakdown and a defensively excellent operator. Played really well against Scotland.
Justin Tipuric 9
His attacking ability is superb - especially in the wide channels. He has the speed of a back and runs like one. Defensively, his low tackling technique compensates for the fact he lacks O'Brien's power
Taulupe Faletau 8
His all-round game is outstanding. He has speed, power and aggression and is similar to Jamie Heaslip in many ways.
Ross Moriarty 7
An unbelievably competitive player who has stepped up to this level and shown he belongs in such elite company