Caster Semenya is an Olympic champion and middle distance runner from South Africa who has been in the press a lot over issues surrounding her gender.
When Semenya was 18, she was asked to take a gender test. The results were not released.
But there were media reports that her test had shown male and female characteristics, including higher than normal levels of a hormone called testosterone.
A hormone is a special chemical in the body which can affect how we behave and how our bodies grow and develop.
Throughout the period of waiting for the gender test results, Semenya was banned from competing, but was cleared to return in July 2010.
The people in charge of making the rules in athletics - the International Association of Athletics Federations (IAAF ) - proposed a new rule that would mean that women like Caster with higher than normal levels of testosterone would have to compete against men or lower the levels of the hormone in their bodies.
The proposed IAAF rule would apply to women who race in track events from 400m up to the mile.
Athletes who want to compete in these events must take medication for six months to lower the levels of testosterone that they have in their bodies, then maintain that level.
The rules were supposed to be brought in on 1 November last year, but were delayed until 26 March after Semenya and her country's athletics organisation - the ASA - challenged the rule, which means this debate will play out in court.
South Africa's sports minister said that Caster had been "targeted" and called the proposed IAAF rule a human rights violation.
Speaking in 2018, Semenya called the ruling "unfair", adding: "I just want to run naturally, the way I was born."
Many people think that Caster has an unfair advantage because of her hormone levels, which they say means that she can perform at a higher level.
In 2016 after Semenya won a gold medal at the Rio Olympics in Brazil, British athlete Lynsey Sharp started crying after she completed the 800m final in 6th place.
In an interview with the Daily Telegraph, Sharp said "everyone can see" the difference between athletes that have higher testosterone levels and those without.
"Everyone can see it's two separate races so there's nothing I can do," she said.
Research paid for by the IAAF in July 2017 found that female athletes with high testosterone levels had a "competitive advantage".
However, critics of the governing body think that the IAAF is treating Caster unfairly.
The IAAF said that the rules are "in no way intended as any kind of judgement on or questioning of the sex or the gender identity of any athlete".
The case is being heard in court from 18 to 22 February, with an outcome expected by 29 March.
If Caster wins she could be free to continue competing the way she has always done, but if she loses the South African athlete could end up not competing altogether, competing against men or having to take medicine to lower her hormone levels.