UFC Star Phil Davis -- Baby Mama Says MMA Makes Him Violent During Sex

10:05 AM PT -- We just spoke to Phil's coach, who told us ... "This is a nasty custody battle, and people are gonna say things that are completely not true ... He's one of the nicest people ... he's a Christian and he's a role model. In fact, he just got back from the Dominican Republic building churches and schools."

And here's a weird one ... Vantris just posted on Facebook that it's all a lie ... saying "Those pictures are not even me ... ." Never mind that she's SAID she filed the same photos ... in court documents.

UFC star Phil Davis has a huge fight Saturday night in New Jersey, but the bigger fight may be May 7 in San Diego, where his baby mama will accuse him of crazy brutality, including violent sex ... and she blames it on martial arts.

According to legal docs -- obtained by TMZ -- Vantris Patterson claims Davis body slammed her on a couch with such force ... when the couch slid into the wall paint came off. She took pictures (below) which she claims show the injuries.

And Patterson says, Davis -- aka Mr. Wonderful -- would often choke her during intercourse, and when she'd plead with him to stop he'd respond, "Shut the f*** up, bitch."

She says Davis has threatened to kill her numerous times if she ever slept with another man.

Now here's the hook -- Patterson claims Davis' alleged propensity for violence has escalated because of his involvement in the UFC. She says, "I am afraid that the numerous fights have negatively impacted his mental stability," and she can't defend herself because of his "increased strength and attacking ability."

Davis makes his own claims ... that Patterson is the violent one who put a pic of a Glock up on Facebook and wrote, "... His day will come." He also says she texted him, "I can't wait until the day you die so I can spit in ur face [painful and slow]."

As for his MMA training, Davis says he's never used his skills outside the Octagon.

When they're in court on May 7, they're both asking for permanent restraining orders and each wants full custody.