Outside Hires Are a High-Risk Option
Stan Van Gundy, Mike D’Antoni, Scott Brooks, Dave Fizdale, and Luke Walton are all former head coaches who don’t have a job as a head coach right now. Stan Van Gundy was hated by most of his players, including Shaquille O'Neal, Dwight Howard, the entire Pistons roster, and Zion Williamson.
Mike D’Antoni has coached Chris Paul, Steve Nash, Amar'e Stoudemire, Carmelo Anthony, Kobe Bryant, Dwight Howard, James Harden, Shawn Marion, and Pau Gasol. That’s nine players who will surely make the Hall of Fame. And he’s never even made the NBA Finals. Is that someone the Spurs want? Nope.
Scott Brooks has made the Finals, but that was with one of the most talented young lineups ever in 2012. Dave Fizdale and Luke Walton have always coached bad teams and never found any real success.
The Spurs could probably pry away a coach who is currently at the helm of an NBA team but predicting who will be on the job market whenever Popovich calls it quits is incredibly difficult. An outside hire might not be the best option for the Spurs by the time he moves on.