BOSTON — A hoodie-clad 16-year-old was chased down in Mattapan Saturday afternoon after police say he bolted from a private driveway with a fully loaded pistol jammed in his sweatshirt pocket.

It was just before 3 p.m. when District B-3 officers rolled up to Woodrow Avenue on a call about a masked crew of juveniles slipping into a yard. The second the blue lights appeared, the group scattered down side paths, forcing one to run headfirst into another officer waiting at the other end.

Cops say the teen had been clutching his hoodie pocket the whole time — inside, an HK P2000SK semi-automatic pistol with one in the chamber, nine in the mag, and its serial number filed off.

Another boy in the group, just 15, had an active warrant — turning what started as a “hang out” into a two-for-one bust.

Detectives confirmed the weapon was defaced, the kind street crews favor when they don’t want their heat traced. The 16-year-old is now looking at charges for unlicensed possession, ammo without an FID, carrying loaded, defacing a serial number, and trespassing.

All this in broad daylight in a neighborhood where front porches face driveways and kids ride past on bikes. Police say this kind of “crew activity” is an all-too-familiar summer sight in parts of Boston — the hoodies, the masks, the thugs scattering the second a cruiser turns the corner.