LoveIs a brown man's fist (1-2)
When love is described as a fist, it seems like it has physical power, and that power is a masculine one. It is a man's fist, after all. It appears this dude is totally in control.
With hard knuckles (3)
This is no weak fist. It has hard knuckles and has probably seen a fight or two before. The question is, do we think this fist is real? It has been described as a metaphor for love, but the more real qualities it gets, the more real it seems.
Crushing the lips, Blackening the eyes (4-5)
These lines give us a clear demonstration of the exact physical effects that the power of love, and a man's fist, can have on a woman. It's the first moment in the poem where a physical power struggle becomes apparent. We can call this a metaphor all we want, but it's hard to deny that someone is getting punched here.