Boston Celtics guard Marcus Smart is one of the best defensive players in the NBA, so he's uniquely qualified to speak on the debate over which player in the league is the most unstoppable.

Smart was posed this question in a recent video done by The Players' Tribune, and his pick for the league's most unstoppable player wasn't Los Angeles Lakers forward LeBron James, Milwaukee Bucks forward Giannis Antetokounmpo or Brooklyn Nets forward Kevin Durant (when healthy, of course). 

It was Kawhi Leonard, who's in his first season with the Los Angeles Clippers after signing with them in free agency over the summer.

Check out Smart's rationale behind choosing Leonard in the video below:

The Celtics and Clippers will square off for the first time this season Wednesday night at Staples Center. It's uncertain if either Leonard (load management) or Smart (right ankle sprain) will play, but if they do, fans will be treated to an epic matchup between one of the league's top five players and one of its finest defenders.

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Don’t miss NBC Sports Boston's coverage of Celtics-Clippers, which tips off Wednesday at 9 p.m. ET with Celtics Pregame Live, then Mike & Scal have the call of the game at 10 p.m. You can also stream the game through the MyTeams App.