A friend of the woman took offense, and a fight ensued, police said.
Police Lt. William M. Tyler said 50 Cent wasn't at the home, which has 19 bedrooms and 37 bathrooms and boasts a gym, billiards rooms, racquetball courts and a disco with stripper poles.
When the woman and her friend decided to leave the mansion, witnesses said, another woman, Michelle Krzykowski, ran after them and grabbed the friend, and McKenzie told her she was attacking the wrong person, according to a warrant for McKenzie's arrest.
Krzykowski hit the woman with a hard object, leaving a large gash in her head, police said. Witnesses told police McKenzie pinned the woman to the ground while Krzykowski hit her.
McKenzie claims the accusation that he urged Krzykowski to attack the woman "is totally false," said his lawyer, Gerald Klein, who has represented him before.
"He's not a celebrity, but he works for one," Klein said. "So I guess he can be targeted by people looking to make hay."
McKenzie, 28, was blasted in the eyes with pepper spray during the fight, Klein said. He faces several charges stemming from the incident and is scheduled to appear Tuesday in Hartford Superior Court, but his lawyer is expected to ask for the case to be continued until Sept. 1.
Krzykowski, of New Britain, also faces assault charges. She's due in court Sept. 1. No published telephone number for her could be found.
50 Cent bought the mansion for $4.1 million. He said it had "a 'Miami Vice' feel," and he spent $6 million on renovations and repairs.
But the rapper, who's from New York City, said he was growing tired of the two-hour commute and put the home up for sale for $18.5 million before dropping the price to $10.9 million this summer.
McKenzie and Krzykowski are free on bond.
Associated Press writer Katie Nelson in Hartford contributed to this report.