Three jockeys were injured at Rosecroft Raceway in Oxon Hill, Md., Tuesday night.
In the fifth race about 9 p.m., Pinderonabender, the lead horse driven by William Carter, took a bad step that triggered the chain reaction accident and involved seven of the nine horses and their carts.
Two jockeys lost consciousness.
Two were flown to a trauma center by Maryland State Police helicopter. They were conscious upon transport. A third was taken by ground to a trauma center.
All three were considered to be in serious condition, but none of the injuries is believed to be life-threatening.
Carter needed stitches around his ears and suffered three fractured vertebrae. Donnie Russell suffered a separated collarbone, which was reset, and has an internal wrist fracture. He was scheduled for surgery Wednesday. Justin Hite suffered a cracked heel and a broken bone on the top of his foot.
The other drivers involved in the accident were treated at Rosecroft.
None of the horses was injured.
Firefighters and paramedics were clear of the scene by 9 p.m.
Rosecroft has live harness racing Tuesday nights. Racing resumed after the crash.
Stay with News4 and NBCWashington.com for updates as they become available.