Tim Duncan during the Finals
Tim Duncan isn't taking it easy in retirement.  USATSI

It's amazing how a person as mild-mannered as Tim Duncan can continuously put himself in some of the most competitive contexts imaginable. A week ago, there was video of Duncan practicing some mixed martial arts, presumably to keep himself in shape with all of his newfound downtime. 

Duncan, however, apparently treats everything like it's his next career.

"He's an animal." Jason Echols -- Duncan's trainer -- told Bleacher Report. " 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."

Echols, who is clearly dying to say fundamentals throughout the interview, went on to talk about actually fighting Duncan.

"Just interacting and punching with him, I hit him with a right hook and his elbow caught the inside of my bicep and tore it right off, just from moving around," he recalled. "Whatever pace I'm at, he sets it. The roaring lion is his passion to learn, his passion to pick up the movements. He's really, really passionate and into the idea of martial arts. It's cool to watch." 

Echols took the next step in his assessment of Duncan as a fighter, with an important caveat.

"He would be a legit competitor. For sure," Echols said. "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."

According to Echols, Duncan had the fire to learn from Day 1, and his passion would explain the rapid growth.

"When he walked in the door, I could see that he was very hungry to learn martial arts, and his movement, his absorption of the martial arts was just phenomenal. You could really see the athleticism that existed in him already."

Fighting Duncan sounds absolutely terrifying. For those that think that he's always a quiet guy that would apologize for nudging you, Echols said that all of that drops when he gets in the ring. "When he walked in, he was always the quiet guy in the public eye," Echols said. "I believe I saw a different side of him, because he's a roaring lion in martial arts."

Ending this with a pitch: Although it's unlikely to see Duncan step in the Octagon any time soon, Duncan stepping in vs. Joey Crawford for a few rounds might become the most-watched Pay-Per-View event since (by then) Mayweather-McGregor. Just a thought.