I’mma shot like a H3, H-U-B-C-I-T-Y, A-B and Y-G
Problem and Hootie nigga

from Kendrick Lamar – Look Out For Detox Lyrics on Rap Genius

Hub City is a nickname for Compton. YG, Problem, and YG Hootie are all from Compton.

“I'mma shot like a H3” refers to a Sony Cybershot DSC-H3 camera.

Alternatively, he could be saying “hummer shot” like a H3. H3 as in the hummer brand car model, hummer shot as in the humming sound you hear when a bullet passes close by your ear. In this context the bullet would come from a HK. Kendrick spits like aa if he were HK (automatic weapon) and his rounds (lines) are coming for your head

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