"Simone Biles has withdrawn from the team final competition due to a medical issue."

Official statement: "Simone Biles has withdrawn from the team final competition due to a medical issue. She will be assessed daily to determine medical clearance for future competitions."

Thinking of you, Simone! pic.twitter.com/QA1GYHwWTv

— USA Gymnastics (@USAGym) July 27, 2021

ADDED: I'm reading "What Happened in Simone Biles’s Vault" (NYT):

Simone Biles balked midway through her vault in the women’s team final on Tuesday, then suddenly exited the competition.... Biles’s absence created a bigger opening for the Russians, who ultimately won the gold.

From the comments there: 

Now the reports are that Ms. Biles withdrew for mental health issues. It is sounding like the pressure affected her performance which is understandable. Heard a "Hidden Brain" feature on choking... and this description of her vault fits into what was being discussed. She began to think about her performance rather than simply do it. Hesitation and balking seem to be symptoms of using her working memory during the vault, i.e. thinking about what she was doing rather than simply letting her body do what she has done many times before.

And, a less sympathetic view: 

If Biles withdrew because of an injury, she was right to do so. If she withdrew because she didn't want to get less than first place, this is unsporting and discredits her good-sportsmanship, even if not her skill.

UPDATE: "Biles... said she pulled out of the event because she wasn’t in the right place mentally to perform the difficult and often dangerous skills she is known for, after feeling so much pressure to be successful. She had been struggling with the stress of being the greatest gymnast in history, she said, and outside expectations were just too hard to combat" (NYT).

The stress of being the greatest? Part of being the greatest is handling the stress. 

AND: The London Times quotes Biles: "I had no idea where I was in the air. I could have hurt myself and it’s very uncharacteristic. So why push it? I just felt it would be a little bit better to take a back seat and work on my mindfulness. I didn’t want to risk the team a medal for my screw-ups because they have worked too hard for that.... I think it shows power in the athlete — protecting my mental and wellbeing that I didn’t want to go out there and do something dumb and get hurt and be negligent.... If you would have said four or five years ago, that definitely wouldn’t have been that Simone — I would have gone out there and did whatever. But today it was like, you know what, I don’t want to do something stupid, get hurt. It’s not worth it, especially when you have three amazing athletes that can step up to the plate and do it. Not worth it.... There comes a time when I have to do it for myself. Coming in today was like fighting those demons. I have to do what’s right for me and not jeopardise my health and wellbeing.”