My'Khyiah Godbolt took the stand at a courthouse in Magnolia, the Daily Leader newspaper reported, to testify against her father, Willie Cory Godbolt.
Godbolt, 37, is charged with capital murder, accused of fatally shooting eight people, including the deputy who arrived at his in-laws' home over the Memorial Day in 2017.
Godbolt's 12-year-old daughter told jurors that he "was very mean" and beat both her and her mother often.
Godbolt appeared agitated, shaking his head and pursing his lips together tightly when she described an attack on her with a plastic bat once when they were practicing baseball outside.
She testified that he became angry when she asked to take a break and beat her repeatedly with the bat. She called to relatives for help, and he responded by threatening her.
"If you ever embarrass me like that again, it's going to be worse," she quoted her father as saying.
Godbolt has pleaded not guilty to four counts of capital murder, four counts of murder, one count of attempted murder, two counts of kidnapping and one count of armed robbery. He has remained in custody since his arrest on May 28, 2017, hours after the shootings.
The killings began after Godbolt entered the in-laws' home in Bogue Chitto and got into an argument with his estranged wife and her family over the couple's two children, a witness testified earlier at trial, according to The Daily Leader.
The witness, Vincent Mitchell, testified that Godbolt fatally shot the responding deputy and then killed Godbolt's mother-in-law and two other people. Godbolt then went to two other homes in south Mississippi's Lincoln County, killing two of his teenage cousins and a husband and wife, investigators have said.
Because of pretrial publicity in south Mississippi, jury selection was conducted in north Mississippi's DeSoto County, 285 miles (460 kilometers) north of Lincoln County. The 12 jurors and three alternates were selected Friday. They are hearing the case in Magnolia, which is near Lincoln County.
The trial resumes Tuesday.