Porsha Williams -- Kicked In The Gut ... By 'RHOA' Co-Star

'Real Housewives of Atlanta' has figured out a way to replace NeNe Leakes ... with a good old fashioned bitch fight.

We're told Porsha Williams was on a boat in ATL with fellow castmate Cynthia Bailey when things got hot. The 2 women began arguing about nothing and Porsha started calling Cynthia a bitch. Cynthia tried to disengage, walking to the other side of the boat, but in true form Porsha followed.

Porsha got in Cynthia's face, and that's when Cynthia exercised self-defense, kicking Porsha in the stomach. Producers came in before Porsha could react and restrained her.

As for injuries ... Porsha went to the hospital, where she scored pain meds.