"I just thought, 'that could be me'. I decided to keep the fact I am gay a secret for a while."
Two years later, Manson came out to his older brother, who is also gay, then to the rest of his family, and then to his rowing mates and closest friends. He finally came out in public last year. The 25-year-old says it felt like a weight was lifted from his shoulders.
"Since I was at school I was terrified anyone would discover I was gay," he says.
"Then when my career took off, I worried the other rowers would find out and it would be all over. I was wrong. It turned out people were more interested in my ability than my sexuality and it was no big deal to most."
High numbers of gay Kiwis also reveal they hide their sexuality. Photo / Christine Cornege
Manson is not alone. The results of the first international research on homophobia in sport, including in New Zealand, is unveiled by the
Herald on Sunday
today and makes for uncomfortable reading - particularly as New Zealand prides itself on being inclusive and was the first in the Asia-Pacific region to legalise same-sex marriages.
The Out On The Fields study focused on sexuality in team sports in Canada, Australia, the UK, Ireland, the US and New Zealand.
About 9,500 people took part, including 631 lesbian, gay, bisexual and straight Kiwis.
One in five New Zealand gay men say they did not play youth team sports and more than half say it was because of negative experiences in school PE classes.
Kiwi gay men are also among the most likely in the world to stop playing sports when they become adults because of discrimination - and 71 per cent believe youth team sports are not welcoming or safe for gay men and women.
High numbers of gay Kiwis also reveal they hide their sexuality. Eighty-eight per cent of young gay men and 76 per cent of lesbian youth say they are at least partially in the closet, keeping their sexuality secret from all or some of their team mates.
The research was initiated by Bingham Cup Sydney - an organisation for gay people in sport - and supported by a coalition of other sports organisations.
Dr Grant O'Sullivan, from Melbourne's Victoria University, was one of seven experts who sat on the study's review panel.
He says a main concern is kids being turned off sport at school. He believes PE teachers in particular need to be trained in ways to support and protect lesbian, gay and bisexual students.
"Often the teachers aren't sure of how to deal with bullying or they may worry about complaints from parents if they talk to students about homosexuality," he says.
Olympic speed skater Blake Skjellerup shied away from rugby in high school due to the intimidating dressing room culture. Photo / Bevan Conley
The results come as no surprise to some of the small number of openly gay Kiwi sporting heroes, such as Olympic speed skater Blake Skjellerup and former NPC rugby player Ryan Sanders.
Skjellerup says he stopped playing rugby at 10 because of an intimidating dressing room culture.
"I love team sports, but I shied away from it during my high school years as the constant homophobic bullying and language used in that environment made me feel isolated and inferior," he says.
"It was easier to come out and be myself in an individual sport because I wasn't afraid of letting anyone down when the only person I was representing was myself.
"We know youth suicide is high and we also know there are higher rates of suicide among gay youth because of homophobia and lack of education. This study clearly shows homophobia in sport needs to be taken much more seriously."
Sanders, who also played semi-professionally in Scotland, didn't feel safe coming out until he retired from rugby in 2004. He started Haka Tours and was named 2010 Young Entrepreneur of the Year.
"I knew I was gay early on but I became very good at leading a double life and hiding my sexuality," he says.
"It's a bit depressing to see the study has found so many gay men still need to do the same while playing rugby and other sports.
"The biggest problem I think is the language. I used to hear the word 'fag' all the time. It sent a strong message that coming out was not an option. It was very stifling."
Ryan Sanders, former NPC rugby player, says homophobic language is the biggest problem in sport. Photo / Doug Sherring
Homophobic language rather than physical violence is the most common form of discrimination, according to the Kiwis who took part in the Out on the Fields study.
Of those who had personally been targeted with homophobia, results show Canadian gay, bisexual and lesbian people were most likely to report being physically assaulted (21 per cent), followed by the UK (20 per cent). Those in New Zealand were the least likely to have encountered violence (12 per cent).
Seventy-eight per cent of Kiwi participants also said they had witnessed or experienced homophobia in sport and just over three-quarters believed an openly gay, lesbian or bisexual person would not be safe as a spectator at a sporting event.
The problem is nowhere near as rife for gay females in sport, insists former New Zealand women's football international Rebecca O'Neill.
The 33-year-old Aucklander is in a long-term relationship and has two kids. She still plays football at premier level for Western Springs.
O'Neill insists she has never had a problem with being open about her sexuality as a player but is more guarded now she is coaching.
"I have never had a bad experience or received verbal insults from other women in sport and never hid the fact I am gay," she says.
"However, because I am coaching, I am now more careful about speaking about it as I realise some people might have an issue with it.
"It is pretty sad that, in this day and age, some people still make derogatory remarks about someone's sexuality."
Rainbow Youth - an Auckland organisation that provides support, information and advocacy for young gay people - believes discrimination has no place in New Zealand sport.
Spokeswoman Toni Duder thinks sports organisations could learn from the New Zealand Defence Force.
In February, the NZDF topped a new global index, ranking armed forces for inclusion of lesbian, gay, bisexuals and transgender soldiers.
Uniformed members have also marched in the Auckland Pride Parade and, in 2012, the Defence Force created OverWatch, a group to support its gay staff.
"What the military has done has really helped change attitudes towards gay people and sports codes could follow the lead," Duder says.
"The fact that so many young gay men, in particular, are not participating in sport or leaving sport early because they feel uncomfortable is a concern.
"They are not only missing out on a lot of fun but could also be denying themselves proper exercise and general fitness, which could have health implications when they are adults."
Robbie Manson advises young people to enjoy playing sport and not feel hindered by their sexuality. Photo / Christine Cornege
Back in his hometown of Thames, rower Manson is training hard to make the Olympics in Rio next year.
He says since coming out in December he has had nothing but support from colleagues, friends and the public.
"When I used to hear homophobic language at school or in sports I took it personally.
"But since I became open about being gay I have realised most people are not homophobic at all. They just use certain language and make jokes about gay people without realising it could be offensive.
"I am not saying this is acceptable behaviour, but I would advise young people to enjoy playing sport and don't let their sexuality stop them," he says.
"Who knows how much talent New Zealand could be losing because young gay people are not participating in sport or stopping it altogether because they think their sexuality will hold them back?
"In my case, most of the concerns turned out to be all in my own head."
Louisa Wall says NZ should commit to ridding sports of homophobia. Photo / Mark Mitchell
Labour MP Louisa Wall is calling for New Zealand sporting codes to join their Aussie counterparts and make a commitment to rid their sports of homophobia.
In a world first, last year all four Australian football codes as well as Cricket Australia agreed to introduce policies to end discrimination.
Big names such as John Eales, David Pocock, Nick Farr-Jones and Adam Ashley Cooper are all rugby "ambassadors" on the issue of homophobia in sport.
Wall - a former representative netball and rugby union player who is openly gay and was behind the gay marriage bill - believes New Zealand should follow suit.
"It is very encouraging that the likes of the NRL and Super Rugby will not tolerate or condone discrimination," she says.
"I would like to see our codes replicate what the Australians are doing and formalise policies to eliminate homophobia."
"I would also like to see this happening in recreational sports in New Zealand.
"These policies should be led by the codes themselves. They should not rely on the Government."
World Rugby and International Gay Rugby recently signed a historic agreement to collaborate on the continued promotion of equality and inclusivity in rugby.
Nick Brown, general manager, public affairs at New Zealand Rugby, says it supports that agreement and promotes rugby as a game to be played and enjoyed by all New Zealanders regardless of race, creed or sexual orientation.
"We would not tolerate any discrimination in this regard," he says.
Rugby Players' Association boss Rob Nichol says homophobic discrimination is not widespread among New Zealand players.
"We focus extensively on the mental wellbeing of players, whether that is providing help and advice about substance abuse, relationships, or behavioural or other mental health issues," he says.
"I suppose sexuality would fall under that umbrella.
"If a player is unhappy or stressed off the field he will not be performing well on it and we would be there to help."
Sporting authorities have already been cracking down on homophobia in Australia.
In March, NSW Waratahs flanker Jacques Potgieter was fined $20,000 by the Australian Rugby Union for calling an opposition player a "faggot" during a match. Potgieter later apologised publicly.
The issue has also made headlines in Britain.
In March, gay Welsh rugby referee Nigel Owens received abuse on Twitter after England's 55-35 victory over France.
