Thomas Davidson, 26, from Florida is charged with assaulting a public servant and criminal trespass.
He reportedly got mad Sunday, when he was told that he couldn't pay for three cell phones with cash.
When the manager refused the sale and asked Davidson to leave, an off-duty officer, who was working security in his DPD uniform, tried to escort Davidson out.
However, witnesses say Davidson grabbed the officer's uniform and pulled him to the ground, straddled him and then punched him.
"[The officer] was the victim in this," said Richard Todd, President of the Dallas Fraternal Order of Police. "He was just asking him to leave and he was attacked."
Court documents say as witnesses tried to pull the 5-foot-10, 225-pound Davidson off, the officer deployed his taser, but it didn't hit Davidson.
Finally, the officer used the weapon as a stun gun, stunning Davidson several times and holding him until backup arrived.
"It's nice to know there are still citizens out there who care about the police and will help the police," said Todd.
But not everyone was looking out for the officer's welfare.
"There were reports they were videotaping while he was being beat up and pounded by the suspect," said Ron Pinkston, President of the Dallas Police Association. "Instead of going to the officer's rescue, there were people who thought it was more important to videotape on their phones than going to help the officer." The officer is a member of the Dallas Police Association.
There is surveillance video from the AT&T store showing the attack, and both the Dallas Police Association and Dallas Fraternal Order of Police want to see it -- but DPD has not released it.
"A lot of citizens don't realize it happens all the time, but this was a deadly force situation and the officer should be commended for not using deadly force," said Todd.
The 30-year-old officer involved suffered a black eye, several cuts and bruises to his face, elbows and knees. He later went to the hospital after showing symptoms of a brain injury.
He's expected to make a full recovery.
Davidson's bail has been set at $125,000.