Houston Texans star Kenny Stills was one of nearly 100 people arrested during a protest in Louisville on Tuesday ... and the WR took his mug shot in a Breonna Taylor shirt.

The 28-year-old NFL player joined 86 others in a massive protest outside the home of Kentucky Attorney General Daniel Cameron to seek justice for Taylor.

As part of the demonstration, the group of people -- which included "Real Housewives Of Atlanta" star Porsha Williams -- sat on Cameron's lawn and chanted ... urging him to levy charges against the cops involved in Taylor's tragic death.

A Lousiville Metro Police Dept. spokesperson says officers eventually told the group to leave ... but when they refused, all 87 were put in cuffs and hauled off to jail.

We're told Stills and the others were booked on 3 charges, including felony "intimidating a participant in a legal process."

As you can see in his mug shot, Stills was clearly NOT happy to be at the station ... and his shirt read, "Breonna Taylors Killers Are Still Police."

The LMPD spokesperson added of the incident, "The protestors chose to occupy the front yard of a home owned by the Kentucky Attorney General and continuously chant towards he and his neighbors."

"At his request, they were trespassed from the property. All were given the opportunity to leave, were told that remaining on the property would be unlawful, and chose not to leave."

Stills has consistently been one of the most vocal NFL players over the years when it comes to the search for social justice ... he's taken knees during the national anthem and has even tatted "Black Lives Matter" on his leg.

According to jail records, Stills was still in custody as of Wednesday morning.