Most Likely, Simple Negligence

According to the Tampa Bay Times, the deputy was working off-duty at Tampa Bay Downs of Friday. When he went to use the restroom his gun went off when he removed his gun belt to set it down.

So here's the deal here. Based on my experience, most duty holsters cover the trigger guard when the duty handgun is resting properly inside the holster. Most properly maintained duty handguns aren't going to discharge unless the trigger is pulled or clothing or something else catches the trigger as the officer holsters the weapon. I suspect the officer's claim that the gun went off when he sat his duty belt on the stall floor is bullshit. Most likely, the officer removed the weapon from his holster while he did the deed in the stall and "boom". I think it's Uncle who, on more than one occasion, has said, "stop playing with it." Good advice and once again, i think the word they're looking for here is "negligently". Just saying.