It's a fight between two Kenpachi's, the 1st vs the present, they previously fought one another with Zaraki losing but wounding Retsu. This time around Retsu is again overwhelming Zaraki, but begins to use different tactics. Zaraki comments on why she is using such cheap tactics this time around, she fires back by saying the last time they fought, she was unable to use those tactics. Inferring that Zaraki has gotten weaker.
Retsu brings Zaraki to the borders of death, probably knowing that it will give Zaraki a burst of fighting spirit and power. That's basically the whole chapter summed up in my perspective, I might be wrong.