I'mma back 'em down like Shaq with this black 2-2-3 in my hand

from Kendrick Lamar – Ignorance is Bliss Lyrics on Rap Genius

Meaning

Backing your opponent down, is a basketball post move. It’s using your weight and strength to get closer to the basket.
Shaquille O'Neal one of the most dominant centers ever, used his size constantly on the post.

.Remmington 223 is an extremelly powerful bullet, used on rifles.

Kendrick makes a comparison between the two. As Shaq was gaining ground in the post by forcing the other player back, his gun will do the same to his enemy.

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