Following the 2015-16 NBA season, San Antonio Spurs star Tim Duncan decided it was time to hang up his sneakers and head into retirement.The quiet giant finished his legendary career with five NBA titles and won the NBA Finals MVP award in three of those series.Duncan will certainly find his way into the Basketball Hall of Fame in a few years, but according to his trainer, he has the talent to give a new sport a try first.Jason Echols, a San Antonio-based trainer, has been working with Duncan on his martial arts skills this past year and recently posted a video of the 7-footer going through some kickboxing drills, as you can see in the video below.

At only 5'10", you can see that Echols clearly has some trouble keeping up with Duncan, even though Duncan isn't going at him with 100 percent effort.

Echols told Bleacher Report in a recent interview that NBA fans wouldn't recognize Duncan when he trains in martial arts, as he ditches his quiet persona for a much more aggressive one:

"Being in San Antonio, it's hard to not know who Tim Duncan is," Echols said. "When he walked in, he was always the quiet guy in the public eye; I believe I saw a different side of him, because he's a roaring lion in martial arts.

"He's an animal. It's a different thing than what you see out on the court. The more intense the training gets, the more calm he becomes, which you've seen on the court. The way he executes the movements, he's a f--king monster."

That's high praise for someone who only recently had the time to start getting more into the martial arts, but it shouldn't come as a surprise that Duncan is good at something he's set his mind to.

Though Echols said he wouldn't advise Duncan to pursue a career in combat sports, he added that it wouldn't surprise him to see the NBA legend dominate if he were to give it a try:

"[Duncan] would be a legit competitor," he said. "For sure. He has a desire to learn and compete. He has the heart for it. He most definitely would be a competitor. I would highly encourage him not to. Being a retired Spurs player, I wouldn't want him going out there and getting punched and kicked by some of those guys, but Tim would be a competitor."

For now, it seems Duncan is content with just training in the martial arts. However, as a lifelong competitor, it'll be interesting to see what happens if he gets the urge to compete once again.