Oliver Brindley, of Doncaster, England, was injured during a multi-bike crash just after 6 p.m. at the American Flat Track "Meadowlands Mile" race, New Jersey State Police confirmed.
Responders said he was unresponsive when placed into an ambulance.
The trouble began when rider Dallas Daniels hit two quick bumps approaching a turn and went down early in the race.
Fellow rider Shayna Texter then hit Daniels's leg and flew over her handlebars.
Brindley "was operating a Yamaha motorcycle when he struck a downed cycle and was thrown over the handlebars," NJSP Sgt. Lawrence Peele said.
Brindley remained in critical condition on Monday, Peele told Daily Voice.
Both Daniels and Texter rejoined the race after it resumed.
"I was actually more concerned about the other riders and hope they are all ok," Texter posted on Facebook.
Several racers had complained about the condition of the track earlier in the day.
"Lots of holes," one said.
Another rider, Nick McFadden, 22, of Owensboro, KY, was also taken to HUMC after losing consciousness in a separate race. He was later released.
American Flat Track bills itself as "the world’s premier dirt track motorcycle racing series and one of the longest-running championships in the history of motorsports," as well as "the most competitive form of dirt track motorcycle racing on the globe."
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