NFL's Marcedes Lewis -- Cops Called In Paternity War ... Baby Mama Allegedly Flips Out

Cops were called to the L.A. residence of Jacksonville Jaguars star Marcedes Lewis Thursday night -- after his baby mama allegedly went berserk when she found out Lewis is gunning for sole custody of their child ... TMZ Sports has learned.

Lewis has a 5-month-old son with porn star Savannah Stern -- who decided to visit Lewis at his pad, which happens to be in a fancy private building in L.A.

We spoke with Lewis who tells us ... Stern was served with court papers during the visit -- informing her that he has filed official documents in an effort to obtain sole custody of their child.

Lewis says Stern began to flip out once she got served -- and began yelling and screaming ... to the point where building staffers decided to call police for help.

Law enforcement confirms ... cops arrived to the scene around 9 PM and took an incident report but no one was arrested. We're told Stern eventually left the building without further incident.