Riot police clashed with protesters in Albuquerque, N.M. on Sunday.

According to USA Today, the protesters were demonstrating against 37 police shootings since 2010 and a recent shooting of an unarmed homeless man on March 16.

While Albuquerque police, who have killed 23 people in less than five years, pushed back protesters, two men who may have served in the U.S. Marines clashed with a demonstrator over an American flag.

A video (below) that has gone viral shows a protester on a motor scooter holding an American flag upside down.

Two men run after him, one of whom is wearing a U.S. Marine T-shirt.

When the protester drops the flag on the ground, the man wearing the Marine shirt picks the flag up and curses, “We serve our f------ country and that’s bull----.”

On YouTube, commenters cursed back and forth over the protester's right to free speech and the man saving the flag.

“I would say the most disrespectful thing that happened in that video is the flag being tossed on the ground,” Marine Maj. Brian Cillissen told KRQE.

“There are a lot of folks that have a lot of passion about that flag and want to protect it at all costs, but that doesn’t negate the fact that we’re in the service to support and defend the Constitution,” Maj. Cillissen added. “If somebody is disrespecting that flag, legitimately it’s not any one person’s place to use intimidation or coercion to try and stop that.”

Sources: USA Today and KRQE