A self-professed member of the Proud Boys from Texas who traveled to Portland, Ore., to confront protesters there last year was sentenced on Friday to 10 years in prison for shooting a man in the eye with a paintball gun, spraying people in the face with bear mace and aiming a loaded handgun at a crowd, prosecutors said.

The Texas man, Alan Swinney, 51, was a “white nationalist vigilante cowboy,” who went to Portland to engage in political violence during protests there in the summer of 2020, prosecutors said.

In social media posts, he made threats against “the left” and “antifa,” prosecutors said, and he tried to recruit people to form a militia to fight in what he believed was a civil war.

Mr. Swinney, who appeared at several demonstrations in the Northwest, became a “known entity” in Portland, as he instigated and committed violent acts under the banner of free speech and pro-police sentiments, prosecutors said.

On two days — Aug. 15, 2020 and Aug. 22, 2020 — he led a small group of like-minded people and engaged in multiple acts of violence during demonstrations stemming from the murder of George Floyd, prosecutors said.

Mr. Swinney caused a serious eye injury by shooting a man in the face with a paintball gun, and he discharged bear mace on multiple occasions — spraying some people directly in the face — and aimed a loaded Ruger .357 magnum handgun at a crowd, prosecutors said. He also shot people with paintballs, prosecutors said.