Usually niggas don't know what to do when their back against the wall so they just start shootin'
T.I. is referring here to two situations, one general and one particular:
You’re poor, you’re desperate, you see no hope of really improving your situation. If you’re a young dude from the ‘hood, chances are you’ll join a gang. After all, what else is there to do?
You’re actually a small time gangster now, you’re in a stressful position (maybe somebody’s mocked you as you were walking by, as described earlier in this song) and you see violence— often gun violence— as the only way of responding.
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