I have mixed feelings about residency requirements for civil service jobs. On one hand I think it's good if people working for the city - especially police - have a personal stake in it. On the other hand, life is complicated and personal relationships can make it difficult for people to stay in one place. If your spouse, for example, has a job elsewhere, it might be difficult to maintain that residency.
But it is pretty nuts that 70% of Baltimore cops don't live there.