Just days after he was filmed shoving a fan at a Colorado Rockies game, a Denver Police Department captain violated the rights of a homeless man on the 16th Street Mall.

Capt. Joe Black will lose four days of time off for violating the man’s First Amendment right to free speech after destroying his sign that read “Need weed,” according to a disciplinary letter obtained by The Denver Post.

An internal investigation found Black did not have grounds to destroy the sign and had changed his story about the incident during interviews, according to the letter.

Black’s actions do not live up to the expectations of Chief Robert White, said Cmdr. Matt Murray, the police department’s chief of staff.

“It’s not consistent with the chief’s vision and the new mission of respecting people,” Murray said. “The chief came here to change a culture.”

Black, who commands the department’s juvenile division, continues to work in his normal capacity, said Daelene Mix, a Denver Department of Public Safety spokeswoman.

The incident between Black and the homeless man happened July 28, six days after Black shoved a fan at Coors Field. A video in which Black shoves Alex Buck three times was shared thousands of times on social media.

In the video, Buck tells the officer he is 22 years old and had three beers. He also repeatedly yells that the officer is violating the rights of an “American citizen.”

Buck was ejected from the stadium but was not charged.

The investigation into the Coors Field incident has not been finalized, and no disciplinary recommendations have been made to the Denver Department of Public Safety’s executive director, who has the final say, Mix said.

She and Murray declined to comment further on the Coors Field incident.

In both cases, Black was working off-duty security.

The homeless man, who was identified only by his last name in the disciplinary letter, was sitting next to an alley on the 16th Street Mall when Black approached him.

Black told internal investigators that the man became belligerent when another officer told him he could not sit or lie on the ground.

The homeless man told investigators that Black had said asking for marijuana was aggressive panhandling.

In a written statement and in an internal affairs interview, Black said he took the sign because the homeless man “might use the sign to swat at members of the public.”

But in a pre-disciplinary meeting, Black claimed he tore up the sign when the homeless man “swatted at me with the sign,” the letter said.

Investigators did not buy Black’s change in the story.

“This self-serving claim made at this late stage of the disciplinary process is not credible,” the disciplinary letter said.

Public safety officials determined the homeless man had a right to hold the “Need weed” sign because it was a protected form of speech.

“Captain Black refuses to take responsibility for his actions,” the letter said.

Because he is a captain, Black is held to a higher standard, Murray said.

“The higher you go up in the ranks, that much more is expected of you,” he said.

Noelle Phillips: 303-954-1661, nphillips@denverpost.com or twitter.com/Noelle_Phillips