Not to defend Buttigieg, but that was a set-up question by an angry black woman interrogator. It was just a way to attack him.
He answered the questions. He said that he told the police chief to not prosecute petty drug crimes, especially marijuana. When pressed on why there were more black people arrested during his tenure, he said that they did prosecute drug crimes when there was violence involved, and they had a problem with violence, shootings, murder, etc.
So basically he said arrests were based on violent crime which was occurring in the black neighborhoods, but no one wanted to acknowledge that, so they said he didn’t answer.
If a person doesn't actually watch a debate, they can’t identify the heavy media spin afterwards.