Ambulances lined up outside the Rio Hotel and Casino on Friday after more than a dozen children, coaches and parents became sick with flu-like symptoms, possibly food poisoning.
Among those sickened were members of the Santa Monica Vikings Tiny Mites. Thirteen children, ages 7 to 12, and five adults were transported to hospitals.
Officials say it may have been a norovirus that caused the outbreak. Flu-like symptoms of vomiting are consistent with cases of norovirus.
Tournament spokesman Justin Gates said that at least nine of the 100 teams participating in the National Youth Football Championships were affected.
The Santa Monica Vikings Tiny Mites won the national championship.
The Associated Press contributed to this report.