​NBA fans were not ready to see Boston Celtics coach Joe Mazzulla putting in the work on the pads in a recent viral clip.Joe Mazzulla is one of the most eccentric figures in the NBA, known for his bizarre comments and approach to coaching.AdvertisementAdvertisementAdvertisementBut for all of his eccentricities, few fans would have expected to see the head coach of the Boston Celtics to be such an expert at boxing.Photo by Maddie Meyer/Getty ImagesFootage of Joe Mazzulla practising boxing in an octagon recently surfaced, courtesy of Ariel Helwani, and NBA fans were absolutely shocked.Mazzulla, who, in fairness, was a former NBA player, therefore a great athlete in the past, has always come across as a composed and passive figure. So to see him this aggressive on the pads had fans taken aback.One fan simply wrote, “Might be the best sleeper build I’ve ever seen.”AdvertisementAdvertisementAdvertisementAnother fan jokingly warned other NBA coaches, saying, “It’s safe to say Joe Mazzulla would win a fight against anyone in the league, including all the players.”“Explains why he talks crazy in post-game interviews,” wrote a third fan who couldn’t fathom what he saw from Mazzulla.A fourth fan joked about the dynamic within the Celtics locker room, noting, “This what he show players that try to take anything other than a three.”But perhaps no fan had a better comment than this one, who noted, “Going with the Wanderlei Silva approach of no straight punches, must be an analytics thing…”Perhaps Mazzulla was so aggressive on the pads because of the frustration he experienced with the Boston Celtics this season.AdvertisementAdvertisementAdvertisementDespite finishing with the second seed in the Eastern Conference, the Celtics were eliminated in embarrassing fashion by the Philadelphia 76ers.The Celtics had a 3-1 lead, but ended up losing out to a young 76ers squad. Ultimately, this series ended up being the end of Jaylen Brown’s time in Boston, as the Celtics surprisingly traded him to the 76ers.With a new squad now, Mazzulla will be aiming to get back to the NBA Finals and prove that it was his system that led them to the championship, and not Brown’s Finals MVP heroics.Read more: