Saturday's ruling comes as the company faces a similar lawsuit in Los Angeles, plus a complaint by thousands of former NFL players against the league and Riddell.
The jury awarded $11.5 million to the family of Rhett Ridolfi, who suffered a concussion during practice at Trinidad High School in 2008. Ridolfi, now 22, wasn't immediately taken to the hospital and now has severe brain damage, as well as paralysis on his left side.
The lawsuit was originally brought against Riddell and several high school administrators and football coaches in Las Animas County, about 200 miles south of Denver near the New Mexico border. The jury assessed 27 percent of the fault for Ridolfi's injuries to Riddell, making the company responsible for paying $3.1 million of the damages.
Three people reached confidential settlements before Saturday's verdict, but two coaches were still defendants at the trial. Ridolfi's lawyer, Frank Azar, said Sunday that he'll ask a judge to find Riddell responsible for paying all $11.5 million in damages.
Riddell said it planned to appeal the verdict but was pleased that jurors rejected allegations regarding helmet design defects.
"While disappointed in the jury's decision not to fully exonerate Riddell, we are pleased the jury determined that Riddell's helmet was not defective in any way," the company said in a statement. It said it believes it designs and manufactures the most protective football headgear for athletes.
Riddell contends that the court erroneously excluded testimony from its warnings expert, though Azar disputed that.
"I think this jury has said they're in very serious trouble," said Azar, who said he is representing between 10 and 20 former NFL players with complaints against Riddell.
In October, a jury in Mississippi found Riddell wasn't responsible for an injury to a high school football player who had suffered a stroke after a practice.