"I stammered, I blinked, I rubbed my eyes. I was just so embarrassed by it and a lot of the feelings that I had as a boy at school came flooding back to me at 28."

A stammer is a neurological condition that makes it physically hard to speak. It is believed that up to 8% of children will stammer at some stage but most will go on to speak fluently. Stammering will be a lifelong condition for up to 3% of adults.

Brown was 11 and preparing to talk in front of his school assembly about a recent ski trip, when he first encountered his stammer.

"All day I was writing a script and I knew exactly what I was going to say," Brown told BBC Sport.

"When I stood up in assembly in front of the whole school - so probably about 100 kids and teachers - I just completely froze. I couldn't say a word, I couldn't say anything.

"I wasn't quite sure why, but I was lucky on that day because one of the teachers saw that something wasn't quite right and so they asked me a couple of questions and as a consequence I was able to get over the block.

"That's the first time I noticed that I spoke slightly differently."

Brown isn't the only high-profile sportsman who has a stammer. Brandon Shell is an offensive tackle for the Seattle Seahawks of the NFL. He told the BBC what it feels like to stammer, or 'stutter' as it is also known in the USA.

"I feel like when I stutter, the word is coming up from my chest and it just gets stuck," Shell said.

"I'm trying to get a word out and I can't. My breath kind of holds and my stomach pulls up and then I have to calm down to get the word out."

What is stammering?

Steph Burgess, NHS speech and language therapist:

"Stammering is an incredibly complex condition - because speech production is incredibly complex.

"When we produce speech, we have to co-ordinate the movement of more than 100 muscles, we have to synchronise that with our breathing because it's the outbreath that powers the movement of our vocal chords and then we shape that out flow with our lips.

"The timing and co-ordination of all of those movements is needed for smooth speech. Because of the differences in the brain of people who stammer, the sounds don't always flow out smoothly."

Stammering and sport

Many elite athletes will list communication as a key attribute for success - which is why some people with stammers might think that team sport isn't for them.

But in reaching the top of their profession, both Brown and Shell say sport has actually helped their stammers. They have found that on the field, stammering was never an issue. For Brown, he puts that down to the team environment and to the quality of his team-mates.

"Sport by its nature is inclusive. Everyone is embraced and everyone is different," Brown said.

"Part of sport is having to communicate with your team-mates and to build a bond with them. And in a good team you have to support each other so it's an amazing environment, I believe, for anyone who has a stammer."

Shell, 29, says being in an environment where he feels confident has had a lot to do with him being able to speak fluently while playing American football.

"I think it helps us doing something, like a sport, that we love to do… we are so confident in what we do, we don't have to think about it," he said.

"I think that's why in football I didn't stutter because I was confident in what I'm saying, and I know it."

Burgess agrees with Shell's analysis.

The NHS speech and language therapist said: "That old mantra of 'feel the fear and do it anyway' holds true for stammering.

"Often the fear is what causes the biggest problems, so if you are doing something like sport that makes you feel good about yourself, it can really improve your confidence."

Dealing with interviews

There is no cure for stammering. If a person stammers into adulthood then their stammer will ultimately be there for life. Instead, people who stammer will often be taught ways to manage the condition through cognitive behaviour therapy or other psychological therapies.

So when Shell entered the NFL Draft process in 2016, not many people were aware of his stammer.

In the NFL, the draft process can be the career-defining moment where young players are chosen by teams for the new season. Alongside the typical physicality and skill tests on the field, they can also be interviewed by any team.

These interviews are just 15 minutes long and can be nerve-wracking at the best of times - but imagine going through this and finding it hard to get your words out because of a stammer?

"You are already under pressure because you are with your potential future employers," said Shell. "There is already some nervousness there. All of a sudden, they ask you something and you just can't get anything out.

"They assume that you are thinking about it but actually I know it and I just can't get the words out right now.

"Then the pressure takes over and I'm like, 'I do know it but I just can't say it, it's not coming out'. That happened to me two or three times in that draft process."

And when asked if people were understanding of it, Shell added: "Well I don't really think that they knew that it was a stutter. It got better as I got older and it just depends how comfortable I was. I coped with it by taking a deep breath and taking my time to talk. When people ask why I talk so slow I tell them it's so that they can understand me."

Brown's advice to those who stammer

Brown is now a coach at Saracens, the club where he played for most of his rugby career. Alongside coaching he also gives after-dinner speeches and motivation talks about overcoming barriers. When asked about what advice he would give to someone who stammers, his answer was a simple one.

"Embrace it," he said. "It's a part of you and it's just how you speak. But never let it hold you back. I truly believe that anyone who stammers can do whatever they want."