The inmate, 31-year-old Mario Christo, was serving a 364-day sentence on charges of disorderly conduct and resisting arrest at the Pinellas County jail when the incident occurred, Pinellas County Sheriff Bob Gualtieri told reporters Tuesday in a news conference.
On Jan. 11, Christo was working in the kitchen and taking out the trash out with two other inmates when he took a cookie from the garbage and tossed it to a bird that was landing on top of the dumpster, Gualtieri said. Upon seeing this, deputy James Moran, one of two deputies who was monitoring the activity, then called out to the inmates, using profanity, asking which one of them fed the bird, Gualtieri said.
When Christo acknowledged that it was him, Moran used profanity again while instructing him to "drop and give him 50," Gualtieri said. Christo dropped down to the ground to start doing pushups, and after completing about two dozen, he became "exhausted" and stopped, Gualtieri said. Moran then walked over and kicked the inmate on his side when he couldn't do any more, Gualtieri said.
He added that it is against jail policies and procedures to issue any form of physical labor or physical punishment to inmates.
"One, there was nothing to punish him for," Gualtieri said. "All he did was toss a piece of trash cookie to a bird."
Christo never reported the incident out of fear of retribution and retaliation, Gualtieri said. When he was released from jail on April 16, he contacted the Pinellas County Sheriff's Office internal affairs division, which found surveillance video after conducting an investigation, Gualtieri said.
Surveillance video shows three inmates wearing yellow uniforms and hairnets as they transfer waste from multiple trash receptacles into a dumpster. After one of the inmates tosses the cookie to the bird, he attempts to walk away from the area, but is stopped by a deputy, who then points to the ground.
The inmate then does several pushups as the deputy watches him before stopping to get into a plank position, seemingly out of exhaustion. The deputy then walks up to him and kicks him on his right side, after which he completed a few more pushups.
Christo told investigators that he was injured and felt as if he had broken a rib, but Gualtieri said there is no evidence of that.
The video left Gualtieri "speechless," he said.
"It is so ridiculous and it is outside the bounds and it is such misconduct," Gualtieri said. "It’s one of the stupidest things I’ve ever seen."
Moran was "immediately terminated." He was arrested Tuesday morning and charged with simple battery for kicking Christo, Gualtieri said. The other deputy, Matthew O'Neill, is currently under an internal investigation for failing to report the incident.
"O’Neill should have come forward as soon as it happened," Gualtieri said.
Moran, 57, was released from jail Tuesday afternoon on $500 cash bond, online jail records show.
When Moran was interviewed, he told investigators that he "didn't really kick him" but rather "nudged" in an attempt to "get him going," and that it wasn't the first time he has instructed inmates to do pushups, Gualtieri said. Moran has been with the Pinellas County Sheriff's Office for more than six years, Gualtieri said.
Moran had one prior disciplinary incident in the past, Gualtieri said. The sheriff did not elaborate on the nature of the incident but said it was not "serious."
Christo was considered a cooperative inmate, Gualtieri said, adding that he otherwise wouldn't have been permitted to participate in the worker's release program, which allows inmates to work time off of their sentences.
Gualtieri said the jail holds an average of around 3,000 inmates, and the sheriff's office has "an absolute responsibility" for their care, custody and well-being, adding that "overall," jail personnel do that "very well every day and respect inmates' rights."
"Unfortunately, it’s another one of those situations where a deputy acted improperly, and he’s been held accountable for it," Gualtieri said.
ABC News could not immediately reach Moran for comment. It is unclear if he has retained an attorney.
ABC News' Rachel Katz contributed to this report.