I heard them chatter: "He's probably young but I know that he's down"
Step on his neck as hard as your bullet proof vest
The police disregard his young age and assume that he’s “down” (gang affiliated), probably just because he’s black. They rough him up based on this assumption, in exactly the same way as the gang members in the first verse.
The fact that they would assume that even a minor is involved in gang warfare also indirectly draws attention to how young most people are when they get into this kind of thing. Being 16 doesn’t indicate at all that he’s too young to be a gang banger.
Kendrick uses a simile, comparing a bullet proof vest, which needs to be strong enough to withstand the impact of bullets, to how hard the police officer is stepping on his neck, illustrating the brutal violence the police in Compton use. It also highlights the difference in power between the authority like them and a kid like himself since he’s just walking unprotected and unarmed (“easily prey”) while they have things like attack dogs and bulletproof vests.
The line of them saying, “He’s probably young but I know that he’s down,” shows the craziness of the cops. You can KNOW when a guy is young, but not know that he’s in a gang. However here, it’s the opposite; they assume with certainty that he’s in a gang without even taking any time to figure out his age.
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