The article says a mattress was taken in and out of the dumpster.

This is basically what precipitated it. It was a dispute over whether the mattress needed to be in or next to the dumpster in order for it to be picked up, and despite everyone being age 30+, there were no actual adults in this whole mess. Important for context though is the fact that Howard had explosive personality disorder, which made him go from 0-100 at the drop of a hat. His angry outbursts clearly contributed to the incident. Also, don't bring a bat to a gun fight.

The article says a mattress was taken in and out of the dumpster.

This is basically what precipitated it. It was a dispute over whether the mattress needed to be in or next to the mattress in order for it to be picked up, and despite everyone being age 30+, there were no actual adults in this whole mess. Important for context though is the fact that Howard had explosive personality disorder, which made him go from 0-100 at the drop of a hat. His angry outbursts clearly contributed to the incident. Also, don't bring a bat to a gun fight.