Semenya returns to 800m at Prefontaine Classic

Caster Semenya returns to the 800m at the Prefontaine Classic Diamond League meeting on Sunday with the athletics world wondering if it may well be her last race over the distance.

The two-time Olympic champion has not raced in the event she has dominated since 2015 since scorching to a world-leading 1min 54.98sec in Doha on May 3.

That outing came just days after the South African star lost a court challenge against International Association of Athletics Federations (IAAF) rules forcing female athletes to regulate their testosterone levels.

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The Swiss-based Court of Arbitration for Sport said while it feared the IAAF regulations were "discriminatory", the measures were "necessary, reasonable and proportionate" to preserve the integrity of female athletics.

Semenya successfully obtained an injunction against the introduction of the new IAAF rules on June 3 after a ruling by the Swiss Federal Tribunal, pending a full hearing.

With no final decision from the court expected until next month at the earliest, it means Semenya is free to run in the 800m at Stanford, which is hosting the Prefontaine as the meeting's usual venue at Eugene, Oregon, undergoes renovations ahead of the 2021 World Athletics Championships.

If the Swiss tribunal eventually upholds the earlier CAS ruling, Sunday's race at Cobb Track & Angell Field could well turn out to be Semenya's last outing in an event in which she has not lost for four years.

Semenya had initially entered the 3,000m at the Prefontaine but instead will now line up in an 800m that she will be expected to win with ease. 

Semenya has been almost four seconds quicker over the distance this year over her nearest rival in Sunday's race, Ajee Wilson of the United States, a winner in the Stockholm Diamond League on May 30.

Elsewhere on Sunday, Christian Coleman heads a new generation of American sprinters who have stepped into the void created by Jamaican icon Usain Bolt's retirement in 2017.

Coleman, 23, is the world's fastest man over 100m this season after clocking a blistering 9.85sec in Oslo on June 13.

Coleman lines up in a field which includes 2017 world 100m champion Justin Gatlin.

Meanwhile in the 400m all eyes will be on rising star Michael Norman, the 21-year-old prodigy who scorched to the season's fastest time -- and joint fourth quickest time in history -- of 43.45sec on his professional debut in California in April. 

Norman is unbeaten over both 200m and 400m this season and could chase a sprint double at the September 28-October 6 World Championships in Doha later this year.

The women's 100m meanwhile sees 2008 and 2012 Olympic champion Shelly-Ann Fraser-Pryce test herself against the emerging talent of American sprinter Sha'Carri Richardson, who turned professional earlier this month after shattering a 30-year-old US collegiate record in the event with 10.75sec.

In the women's 200m,  Jamaica's 2016 Olympic champion Elaine Thompson attempts to lay down a marker ahead of the World Championships when she faces Britain's Dina Asher-Smith in a field that also includes Dafne Schippers of the Netherlands.