A 24-year-old man who authorities say was among masked Antifa supporters attacking conservatives at a June demonstration in Portland, Ore., was sentenced Friday to nearly six years in prison in connection with a brutal baton assault.

Gage Halupowski pleaded guilty to second-degree assault after authorities accused him of using a weapon against a conservative demonstrator who suffered blows to the head that the victim claims left him with a concussion and cuts that required 25 staples to close.

PORTLAND MAYOR DISTANCES SELF FROM ANTIFA VIOLENCE IN HIS CITY: 'I WASN'T EVEN HERE'

After the assault, police saw Halupowski collapse his metal baton and conceal it in his pants, FOX 12 Oregon reported.

The attack outside a Portland hotel on June 29 was “completely unexplainable, completely avoidable and didn’t need to happen,” Multnomah County Deputy District Attorney Melissa Marrero said, according to OregonLive.com.

Authorities say Halupowski attacked Adam Kelly as Kelly was attempting to help another man who’d been assaulted, the news outlet reported.

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Halupowski’s defense attorney, Edward Kroll, called his client’s prison term “one of the harshest sentences I’ve seen for someone with no criminal background and young age,” but acknowledged that having the attack caught on video left Halupowski with few legal options other than accepting a plea deal.

Marrero disagreed, calling the sentence appropriate for Halupowski’s crimes, according to OregonLive.com.

Charges dropped under Halupowski’s plea agreement included unlawful use of a weapon, attempted assault of a public safety officer and interfering with a peace officer, the outlet reported.

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The attack against Kelly occurred the same day that a group of assailants attacked conservative writer Andy Ngo, dousing him with liquids and pelting him with objects, with those attacks also caught on video.

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Ngo claims he was later hospitalized with a brain hemorrhage and says no suspects have yet been charged in connection with the assaults against him.

Violent clashes between Antifa supporters and members of conservative groups have been a vexing problem for the city of Portland, whose mayor, Ted Wheeler, has faced harsh criticism for the city’s response to such events. President Trump and some Republicans in Congress have called for Antifa to be declared a domestic terror organization.