By Alan Baldwin

LONDON (Reuters) - If misfortune were to prevent New Zealand rider Jonelle Price from competing in the Rio Olympics, her husband Tim will take her place.

Should anyone else pull out, the couple will form half the eventing team.

Only in the equestrian events, where men and women ride together as a team while also chasing individual medals, could such a situation arise and even then it is unusual.

While other sports -- tennis, badminton and sailing's Nacra17 class -- have mixed events involving pairs, replacements cannot be just slotted in and in any case would have to be of the same gender.

Jonelle, 35 and a team bronze medalist in 2012, is in the four person NZ eventing lineup for the Games while Tim, 37, is the official traveling reserve along with 13-year-old horse Ringwood Sky Boy.

The British-based couple both want to win, which cannot always make for easy conversation over the breakfast table at their Marlborough base, but are also hugely supportive of each other.

"We’re both fiercely competitive and we work day in and day out with each other in the same environment and that definitely has its challenges," Tim Price told Reuters.

"But we’ve overcome those things and found a way to make it an advantage.

"We can flip it any old way...if I was on the team with Jonelle, then that would be an advantage and a strength. And likewise if I’m the support crew, which I am at this stage, that will be the role I’ll take on and it will be an advantage as well."

Price was a World Cup showjumper before moving to eventing and heading to Britain with Jonelle in 2003 for the Burghley Horse Trials.

In 2014 they became the first husband and wife to represent New Zealand together at the World Equestrian Games.

Jonelle was New Zealand's best individual performer there, finishing fourth.

"The ideal scenario is that we are both riding the peak of the wave but it is horses and it doesn’t always quite go to plan," said the rider, who broke her arm in a fall five weeks before the London Games.

"You’ve got to be able to take the down time as well as the good time and put your personal disappointment aside and be supportive to the other person.

"Tim’s in that boat at present, come two years down the track it will possibly be me."

There can be the occasional argument over a horse, even if they are rarely looking for a similar mount due to physical differences such as height and strength. And the couple have been together for more than 16 years.

Eventing is a sport where horse and rider qualify together, so that if the animal develops an injury or sickness then both are ruled out.

That means the weeks before the first day of competition are tense, with plenty that can go wrong even after the animals arrive.

Tim Price recognized his position was a tricky one, particularly if his chance were to arise from his wife's misfortune.

"There would be a bit of a hat being thrown on the ground but then once you get over the initial disappointment you crack on with what we’ve got to go for," he said.

Not that he is expecting any such situation.

"I was the water boy in London...I just went to support Jonelle and the team," he said. "I was involved in the world championships two years ago. It’s a privilege to be involved in this one."

(Reporting by Alan Baldwin, editing by Toby Davis)