Spears yelled "I am going to kill you!" and cursed at Andrew Deetz, a photographer who was allegedly beaten by Spears' bodyguard on Thursday, according to a statement released by their lawyers.
Deetz, 24, and another photographer, Kyle Henderson, 23, said they were preparing to sue.
The men were taking pictures of Spears, 25, as she and her children — 22-month-old Sean Preston Federline and 10-month-old Jayden James Federline — left the spa at the Wynn Las Vegas casino-hotel at about 11:30 a.m., accompanied by two bodyguards.
As they were about 30 paces away and walking in the opposite direction,, threw him on the ground and punched and kicked him until security pulled him off, it said.
Afterward, Spears ran toward Henderson but was stopped by security, and then threw a baby bottle at him, it said.
Then, in front of several other hotel guests and bystanders, Spears threatened to kill Deetz and said he should get a restraining order against her because she was going to kill him or hire someone that would, it said.
Spears' lawyer Gary Stiffelman declined to comment.
Wynn Las Vegas released a statement confirming that Spears stayed at the hotel and left on Thursday, but also declined to discuss the confrontation.
"We respect the privacy and do our utmost to maintain the anonymity of our guests," it said.
Las Vegas police issued a summons for a charge of battery to Camera, the only person cited. He could face up to six months in county jail and a $1,000 fine if convicted.
Stiffelman's office would not relay messages to Camera seeking comment, and The Associated Press was unable to find a phone number for him.
By Ryan Nakashima