With his brother Pasquale (Pat), Petronelli managed and trained world middleweight champion Marvelous Marvin Hagler.
[1] The Petronelli brothers opened their Brockton gym in 1969, the same year both Marciano and Colombo died (in a plane crash and an auto accident respectively.)
Petronelli focused on training fighters, relying on his Navy medical experience as a cut man in the ring, while Pat mainly handled the business aspects, including fight scheduling and purse negotiations.
Though Hagler was a top-ranked middleweight title contender for most of the 1970s, the Petronellis found it difficult to line up high-profile opponents willing to risk facing him.
Petronelli and his brother finally got Hagler his shot at the WBA and WBC middleweight titles in 1979 against Vito Antuofermo in Las Vegas, where the fight was ruled a draw in a controversial 15-round decision.
In 1980, after winning 50 of 54 pro fights, Hagler got his second chance at the crowns when he faced British fighter Alan Minter, who had earlier won the title from Antuofermo.