Cut my leg off, I wouldn’t be defeated

from J. Cole – Atlantic City Freestyle Lyrics on Rap Genius

This is a double entendre.
First, even physical violence isn’t enough to ‘defeat’ J, you need to beat him lyrically before you can say you’re triumphed over him.
Second, he’s saying even if you cut off his leg, he won’t be de-feeted, which is a literal meaning of having his feet cut off.

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