Corporal Eric Casebolt was seen pulling the 14-year-old girl's hair and pinning her down for several minutes, shouting "On your face" as he shoved her head into the grass.
"Call my mama, oh God!" she shouts, CNN reported.
He forcefully swings her by her arm to the ground.
"On your face!" he orders and presses his open hand to the back of her head and slams her face-first into the grass.
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The case comes amid growing unease across America over the use of violence by police officers, especially against black people.
Casebolt, an officer of 10 years with experience in martial arts, was named Patrolman of the Year in 2008 in McKinney, a city of 150,000 people.