Fiery NRL legend Mark Geyer says anger was a huge driving force during his footy career, and while his aggression was both a benefit and a curse, experts say anger is a key tool for training athletes.
Mark Geyer was only 17 when he was "kind of thrust into the spotlight of being the hit man."
In fact, for a period in his twenties Geyer had earned the title as the most suspended player in rugby league history, after being sidelined for 34 weeks.
As the youngest player but standing at a towering 195cm, the couch quickly nicknamed him Mountain. Geyer embraced the role of being the team's intimidator and saw it as a great badge of honour.
"I quickly became the person who was the angry man on the field … I'd go out on the field without any rules and regulations and play accordingly and it got me into a lot of trouble."
And who could forget Game Two of State of Origin in 1991 when it exploded into violence after Geyer tackled Steve Walters just before half time. The resulting confrontation between Geyer and Wally Lewis is often included in the list of iconic Origin biffs.
"When you're in such a cauldron when it's 40,000 people just cheering and wanting you, especially against Queensland in State of Origin and driving rain, against the best player in the game in Wally Lewis, and I'm 22 years of age and face to face with him and he's calling you every name under the sun and you're doing the exact same back to him, it's an out-of-body experience."
Born in 1967 to teenage parents, Geyer lived in a rented fibro housing commission house before settling in Penrith. He said growing up in Mt Druitt and getting rejected from jobs because of his postcode gave him a bit of a chip on his shoulder.
Rugby was a release and a way to channel his aggression, although his anger was both a benefit and a curse, whether it was on or off the field.
"When you can't sleep after a game, you're awake, you have a couple of beers and you feel drunk because you're so fit and the littlest things annoy you. Well in my case they did and the littlest things people would say to me I'd take to heart … I'd chase people 10 in my car just to find out where they lived … I wanted them to know that I knew where they lived. Stupid really."
"My hardest part about being a professional rugby league player was turning the switch off after I come off the field."
"You're 10 foot tall and bullet proof, nothing could hurt you because you're playing in the hardest sport in the world and you're not getting hurt by the biggest men in the world so that means that everybody off the field insignificant when it comes to the power game, and I played that card pretty well."
"My hardest part about being a professional rugby league player was turning the switch off after I come off the field. Going to the nightclub and seeing blokes, alpha males as well, who, it's like animals; you're marking your territory. If someone tried to come across in your territory there'd be an altercation and nine times out of 10 the next day I'd be hanging my head in shame," Geyer said.
Anger is often viewed as a negative emotion - unproductive and destructive. People seek to minimise it or transform it into something more useful. But what if this emotion is actually good, and can we use it for positive gain?
"I heard one characterisation about how anger is an irrational emotion and I've got to tell you I don't really think that that's true."
"I think that every emotion that exists in us is not rational or irrational, they're functional … the fact that the anger has existed in us and currently exists in us means that it was functional for us in some way, shape or purpose in our evolutionary history," Matsumoto said.
"I define anger as an immediate reaction to an event that has caused the person to believe that they've lost, there's an obstacle to some kind of goal of theirs and so the anger is a reaction that primes a person to be able to do something in order to remove that obstacle."
As head coach of the US Judo team for the 1996 Atlanta Olympic Games and a team leader for 2000 Sydney Olympics, Professor Matsumoto believes anger is a very important emotion to use when training athletes.
"The origins of many sports to begin with are ritualised versions of something related to battle. So it makes perfect sense to people to pump themselves up or need to pump themselves up for peak performance by emulating or even becoming angry.
"So certainly anger plays a large role in the optimising one's performance because it's so physical in many sports and many sports like rugby and like Judo is actually battle with another person. So being angry to some degree is actually very helpful and very useful."
"Anger plays a large role in the optimising one's performance."
From his observations, it's the competitors who feel angry and not dejected or emotionless after a loss, that harness the anger to better their performance.
"The ones that are angry are usually the ones that are really motivated to get better and they'll do better and they'll sustain that motivation longer."
Mr Matsumoto said it's the coach's role to guide the athlete's transition back into normal life, and help them learn to differentiate between aggression on and off the field.
"As a coach it becomes very important to find everybody's optimal zone of performance and thus their optimal zone of that motivational level of anger. And everybody's different about that but every coach has got to find it, every athlete has to find it ... and ritualise that behaviour so that when you get to game day, you know exactly what you're going to do to be able to have that peak performance."
These days, Geyer isn't the hot-headed young man that he was, and said fatherhood definitely helped mellow him.
"Now I'm on breakfast radio ... I'm a big soft cock really. Excuse me. Like I am so opposite to what I was, it's unbelievable," the father-of-five said.
"I still wouldn't back down from a fight now if someone stepped over the line and encroached upon my space, but I don't go over to their space. I don't go looking for trouble, I don't go looking for the ways to be a he-man, them days are way gone. These days I'm a very passive man."
"I'm a big soft cock really ... These days I'm a very passive man."
"Like the old Mark was very volatile and when you asked him out to give a rate out of 10, I was 11 out of 10, off the Richter. For a five-year period then I was the most angry man, I felt like the most angry man on the planet but now I'm about a 3 or a 4."
"I think if I had to really categorise why I did come good and why I haven't been in trouble for a long time is because of my children. I want to be a great dad," the 47-year-old said.
"I've had to learn to temper that, and that's a lot of talking with my wife about, and we speak now more than we've ever spoken to each other and I really think that's the metamorphosis that I've overtaken."
Mark is a guest on this week's Insight program. Join guest host Anton Enus, television chef Adam Liaw and restauranteur Matt Kemp as we look at how anger works in the brain and in society.