DENVER – The school walkout by Denver high school students this week took an ugly turn when four officers protecting the marchers were hit by a car.

But the ugly turn wasn’t that they were hit by a driver reportedly having a medical emergency, it occurred when witness say the protesting students cheered. That’s the charge of the Denver police union.

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Students allegedly chanted “hit him again” after one officer was struck and critically injured.

The Denver Police Protective Association denounced the incident as “quite possibly the most disturbing thing this association has ever heard,” according to the Denver Post.

Denver students walked out of several high schools to protest the grand jury decision in Ferguson, Missouri.

Officer John Adsit was hit by a sedan and dragged “dozens of yards,” according to the paper.

He’s spent six hours in surgery so far and is scheduled for another one operation. The life-threatening injuries have reportedly been dealt with.

“This group of high school students not only broke DPS rules by leaving school without authorization, but broke laws of the City and County of Denver and State of Colorado regarding traffic regulations and the right to assemble with a permit,” a statement from the police union reads.

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“The DPPA recognizes citizens’ rights to assemble lawfully. This, however, was not a lawful assembly, which ultimately cost four Denver Police Officers a trip to the hospital. One of which is in critical condition.”

Meanwhile, Fox 31 reports while students were “chanting disrespectful terms” after the officers were hit, “sources say they saw teachers standing by while this happened, and they did not intervene.”

Denver Public Schools released a statement saying, “We have no knowledge of the alleged comments. We would deplore any such comments and will look into the allegation, and would welcome any evidence that would assist us in an investigation.

“All afternoon yesterday and all day today, students at East expressed their deep concern for Officer Adsit and his family and their appreciation for the police assistance in ensuring student safety during the march.”

Denver Police union president Nick Rogers says some officers “personally heard” the statements from students, though they would not speak on the record about it.

“Not in this environment,” Rogers tells the news station.