During a social gathering on Saturday, the girl went inside the family's home in Shiner while other members of the family were tending to horses outside, CNN reported.
The father caught a 47-year-old man -- with whom he was casually acquainted --attempting to molest his daughter, Lavaca County Sheriff Micah Harmon told the Victoria Advocate. The father then allegedly punched the man in the head until he died, Harmon reported.
The father and daughter weren't named to protect the identity of the 4-year-old girl. She was described as "ok, besides the obvious mental trauma" of the incident, Harmon said.
The alleged abuser was found dead at the scene. His name wasn't released pending the announcement of his death to his family.
The sheriff's office will defer to a grand jury to decide whether charges will be brought against the father.
"You have a right to defend your daughter," he told CNN. "[The girl's father] acted in defense of his third person. Once the investigation is completed we will submit it to the district attorney who then submits it to the grand jury, who will decide if they will indict him."
The father was reportedly "very remorseful" about the death and did not know the alleged abuser would die of his injuries.