Apparently, Toni's shame that "weighs down" his ma is enough for her to call a hit to kill him, and now you've gotta gun down every hitman.
These always travel in waves of four, the first wave wielding Pistols. The next wave you advance have more hardcore guns. You've gotta watch out for Grenades and there's some weapons ammunition lying around. Once you've took out all of the hitmen, you pass the mission.
Reward: Money dropped by hitmen, weapons and ammunition pickups
From now on, hitmen will be after you. Now and again, they'll try to kill you and chase you, and when they do you can either kill them or evade them. If you kill them, they'll drop their weapons (like AK47s and Macs), money and Body Armor.