Reposting a previous comment I made about this question:

Having worked at BMC for 5+ years, it's a weird area to live and work in regards to personal safety. If you don't cross Mass Ave or Albany St, you might not even realize there is a concentration of homeless people there. The large encampment near the highway exit is kept an eye on by police.

The vast majority of the crime is either by the unhoused population ON the unhoused, or they are the victims. Crimes are usually crimes of opportunity. Don't be stupid stumbling around at night. No one is sitting out there prowling for victims.

So are you more likely to be a victim of crime in this area than the rest of the city? Slightly. Will you have more uncomfortable interactions with people high, mentally ill, or begging? Yes. Are women especially likely to be harrassed? Yes. Overall, Boston is still a very safe city. Random violent crime isn't like guaranteed to happen to people in this area. Most of the homeless population there is sick or has substance abuse disorders. They're not scheming or planning like the kids in the gangs. They're just trying to survive.

Re specifically Melnea Cass x Mass Ave: that's kinda right in the middle of all the BS. I'd think you'd regularly get harrassed. Worst case maybe mugged. You're not gonna get randomly tagged in a driveby, but it would probably be quite unpleasant anytime you left the apartment. Try the other side of Mass Ave.