The altercation took place around noon Tuesday in a common area of the Bristol County House of Correction in Dartmouth, where only one inmate is supposed to be out of his cell at a time, Sheriff Thomas Hodgson said.
It's unclear which inmate was the aggressor. Hodgson said jail staff are interviewing witnesses and reviewing surveillance video to figure out exactly what happened and determine whether disciplinary measures or even criminal charges are warranted.
"It was very brief. The officers were right there and it was stopped within seconds, maybe a minute," Hodgson said.
The jail is also reviewing procedures to figure out how the two inmates were allowed out of their cells at the same time.
Hodgson did not release the other inmate's name and said he did not know of any previous tension between the two men.
"We don't know what, if any, relationship there was or has been at any point, either here or anywhere else," Hodgson said.
Both Hernandez and the other inmate have been moved to other units until the investigation is completed.
Hernandez, a former New England Patriots tight end, is being held without bail after pleading not guilty to murder in the death of 27-year-old Odin Lloyd. The Boston man was dating the sister of Hernandez's fiancee.