This went down Saturday in City Center Park, where a musical vigil had been planned to pay respects to Elijah -- who died while in custody of Aurora PD last year -- which was incredibly symbolic, seeing how Elijah played violin himself. At one point, the police had seen enough.

In the video, captured by a vigilant bystander, you can see the jarring juxtaposition play out live on camera. At first, you hear the violinists -- some of whom are said to have been underage -- beautifully playing in unison, and the next minute ... cops are storming the place.

The woman recording can be heard -- along with others -- openly yelling "No!" at what's about to happen next ... forcible removal and literally pushing the protesters out of the park, while shutting down the performance. Pepper spray started getting dispersed at one point too.

A reporter on the ground captured an even more surreal moment ... as cops were literally pushing up against protesters, a violinist on stage started playing soothing melodies.

The protesters stood their ground as long as they could -- several even formed a human barrier around the violinists to protect them from the police. Communal chants also erupted ...  with phrases like, "Why are you in riot gear? I don't see no riot here!"

Eventually, the protesters were forced to the parking lot ... but they didn't let that ruin the get-together. Some violinists followed along and continued on the pavement. The protesters even broke out in song, singing "Lean On Me" ... in what proved to be a powerful statement in response to the brutality they'd just gone through, for no reason at all.

If you're wondering what Aurora PD had to say about this, they claimed the crowd was getting unruly and some were even arming themselves and hurling projectiles at the squad. In the end ... the police say only 3 people were arrested for violating lawful orders after warnings were given.