Why was Simona Halep’s doping suspension reduced? And when can she return to playing tennis?

Simona Halep is allowed to resume her tennis career whenever she wants, now that a four-year doping suspension was reduced by the Court of Arbitration for Sport to nine months — and the two-time Grand Slam champion already has missed more time than that.

"I cannot wait to return to the tour," Halep said.

The ruling on her appeal came Tuesday from a three-judge panel at the court based in Lausanne, Switzerland, so it's too soon to know when to expect to see Halep back in competition. And CAS, as the highest judicial body in sports is known, did not release its full findings yet, just a summary, so it's also too soon to know all of the ins and outs of the reasons behind the decision.

Here is what you need to know about what happened:

Halep is a 32-year-old from Romania who has reached the pinnacle of her sport, reaching No. 1 in the WTA rankings and winning major championships at Wimbledon in 2019, by beating Serena Williams in the final, and at the French Open in 2018, by beating Sloane Stephens in the final. Halep's game is built primarily on defense and speedy court coverage.

Halep tested positive for the banned drug Roxadustat at the 2022 US Open, where she lost in the first round to Daria Snigur of Ukraine 6-2, 0-6, 6-4. It was the first tour-level win of Snigur's career. Roxadustat was approved for use in the European Union in 2021 to treat the symptoms of anemia caused by chronic kidney failure. It stimulates the body to produce more of the natural hormone erythropoietin, or EPO, which has long been a doping product favored by cyclists and distance runners to boost stamina. She was given a four-year ban that would have expired in 2026, in all likelihood meaning the end of her professional tennis career.

WATCH: Tennis Channel Live reactions to Halep's case ruling and CAS decision

Halep, who was represented by lawyer Howard Jacobs, argued that she was exposed to a contaminated supplement, which caused her failed test. CAS determined Halep bore "some level of fault or negligence" for not exercising "sufficient care" while using the supplement, but "she bore no significant fault or negligence." So that is why, CAS said, "her anti-doping rule violations were not intentional."

In October 2022, Halep was provisionally barred from her sport because of the test that year. Then, in May 2023, she was accused of a second doping offense by the International Tennis Integrity Agency for irregularities in her Athlete Biological Passport. Those passports provide a baseline reading of substances in an athlete's body and are considered a way to help chart doping, because fluctuations over time raise red flags. The ITIA wanted her initial punishment to be extended to six years in total. But Tuesday's ruling mentioned two tests she took about two weeks apart in September 2022 that led CAS to be "not comfortably satisfied that an anti-doping rule violation" related to her passport had occurred.

Probably not. Jacobs, Halep's lawyer, said Tuesday that the athlete "has already initiated a lawsuit against the supplement company." Jacobs also pointed out that the CAS panel's decision means her suspension would have ended in July 2023, so she "should have been eligible" to play in last year's US Open and this January's Australian Open. The next Grand Slam tournament is the French Open, which begins in May.

"Throughout this long and difficult process, I have maintained my belief that the truth would eventually come out, and that a just decision would be reached, because I am and always have been a clean athlete," Halep said in a statement released by Jacobs. "My faith in the process was tested by the scandalous accusations that were leveled against me, and by the seemingly unlimited resources that were aligned against me. But in the end, the truth prevailed, even if it took much longer than I wish it had."

Howard Fendrich has been the AP's tennis writer since 2002.