To the casual observer – and at the risk of using “casual” in any sentence with rambunctious rookie Isaiah Stewart as the subject – it’s been easier to spot the offensive evolution of the Pistons 19-year-old center than it has his growth defensively.

But it’s there, noticeable to the folks who matter most and greatly appreciated by Stewart’s coaches and teammates.

It starts with his physical toolkit – nimble feet, a 7-foot-4¾ wingspan and strength that belies his birth certificate – but is tied with a double-knot bow by his tenacity and fortitude. And now it’s been supplemented by a spin through the NBA, Stewart topping 1,000 minutes in Saturday’s game at Portland.

“Night and day,” six-year veteran center Jahlil Okafor says of Stewart today vs. Stewart in training camp at the defensive end. “He’s picked up everything very fast.”

Stewart leads all NBA rookies in rebounds per game (5.9), offensive rebounds per game (2.2), blocks per game (1.0) and shooting percentage (.569). He’s doing that in a little less than 20 minutes a game, though Stewart’s minutes have inched up month over month as he earns a broader role while his offense and defense grow more diversified and reliable.

To that end, Stewart’s recent success as a 3-point shooter has generated keen interest. He hit another in Sunday’s wildly entertaining loss to the Los Angeles Clippers in his only try.

To be sure, a center who shows the potential to be an above-average 3-point shooter opens up a world of possibilities for his team’s attack. But Dwane Casey is inclined to wait on the 3-point shot and focus more on the meat and potatoes of Stewart’s game: rebounding, protecting the rim, suffocating pick-and-roll plays, screening and using his voice. On that latter point, Casey has seen – heard, rather – Stewart make great gains.