And by the time you all catch on, I'mma end your career
And walk away with the whole floor so you have nothing to fall back on
Another clever bit of wordplay. Usually, when rappers or singers are starting out, they have a day job, and just do the performance bit on the side. In other words, they have another career to ‘fall back on’ if things go tits up in the music industry. Eminem is going to take the floor away so anyone he defeats in a battle literally won’t have anything to fall back on.
We can read “walk away with the whole floor” metaphorically as well as literally. When a public speaker “has the floor” it is their turn to speak and they have the attention of the audience, so to “walk away with the whole floor” suggests that Eminem has 100% of the audience on his side, leaving nobody to support a competitor.
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