Defending champion taken away by ambulance after incident
Defending champion Fields, 28, needed medical attention after the scary incident in the third heat of the semi-final of the competition at the Tokyo Jeux.
Three bikes crashed on the first turn of the final semi-final run, and Fields received treatment before being taken to an ambulance, according to Olympics.com.
Fields landed hard from a jump and lay on the ground, with his Team USA jersey ripped as medics ran to treat him.
The semi-final round of the competition had been delayed for 45 minutes because of rain.
The men’s final was set to go ahead without Fields with a field of just seven riders.
The incident involving Fields was then followed by another crash in the third run of the women’s semi-final.
Australia’s Saya Sakakibara was leading the race when she crashed and had to also be stretchered off.
Fields became the first American BMX rider to win a gold medal in the event at Rio 2016.
He made his Olympic debut at the 2012 London Games, where he finished seventh in the event.