Casebolt's lawyer informed FOX4 of Casebolt's decision on Tuesday afternoon.
McKinney Police Chief Greg Conley said Casebolt's actions were "indefensible" during a Tuesday evening news conference.
"He came into the call out of control and as the video shows was out of control during the incident." Conley said. "I had 12 officers on the scene and 11 of them performed according to their training."
The video of the Friday incident involving Casebolt at a McKinney neighborhood pool went viral and had initially landed Casebolt on administrative leave while police officials conduct an investigation.
Casebolt was seen pulling Dajerria Becton to the ground and pinning her with his knees while she cried out. He also pulled out his gun and pointed it at other teens and briefly ran after them before being stopped by two fellow McKinney police officers. Throughout the video Casebolt is heard repeatedly cursing.
"Our policies, our training, our practice do not support his actions," Conley said.
Mayor Brian Loughmiller said Tuesday during the press conference that the "incident is not indicative of McKinney as a whole."
Casebolt had served in the Navy for a decade from 1993-2003. He was an operations specialist for seven years and in the military police for another three years.
From 2003-2005 he was a highway patrol trooper with the Texas Department of Public Safety.
Casebolt's now-deleted LinkedIn account stated Casebolt joined the McKinney police force in 2005.
Casebolt was also listed as an instructor at the McKinney-based Executive Self-Defense & Fitness Training. Its listing said Casebolt had trained in "several different disciplines of martial arts, but now exclusively trains in Krav Maga combat arts, Arnis, and ground fighting."
The company has since deleted any reference to Casebolt from its website.
There is still an investigation into a fight that happened about 30 minutes or so before the incident with the 15-year-old.
Two women, one of whom is reportedly a resident, got into it with a party promoter. Online, the party promoter says the woman yelled racial slurs.
However, a friend of the resident told FOX 4 on Tuesday that that's out of character.
Another rally was held at the McKinney Police Department on Wednesday night.
Religious and civic leaders and citizens at the rally said that they were relieved that Casebolt had resigned and that charges against the only teen arrested during the incident had been dropped.