Stephon Castle’s trainer Olin Simplis believes the San Antonio Spurs guard has already established himself as the NBA’s most versatile perimeter defender and has the tools to become an All-Star and All-Defensive selection in his third season.
“I honestly think he’s the best perimeter player,” Simplis told Mark Medina of R.org, pointing to Castle’s ability to defend positions across the floor. Simplis said Castle’s combination of size, mobility and defensive assignments separates him from other guards.
Castle, listed at 6-foot-7 and 215 pounds, averaged 16.7 points, 7.4 assists and 5.3 rebounds in 68 regular-season games during 2025-26. His workload expanded substantially from his Rookie of the Year campaign, while San Antonio finished 62-20 and reached the NBA Finals.
The Spurs ultimately lost to the New York Knicks in five games, and Castle struggled offensively in the series, shooting 37.7% from the field and 30% from three-point range. Simplis attributed part of those issues to the physical demands of Castle’s two-way role.
“He’s guarding the guys that are the primary scorer on each team,” Simplis said. “Then when that player is out of the game, he guards power forwards and centers as well.”
Castle averaged 30.0 minutes per game in the regular season and 33.0 in the playoffs. His postseason production increased to 18.2 points, 6.1 assists and 5.0 rebounds per game, while he shot 45.9% overall and 35.0% from three across 23 appearances.
Simplis highlighted Castle’s defensive versatility as the strongest part of his development, citing matchups that ranged from Shai Gilgeous-Alexander and Anthony Edwards to Julius Randle, Karl-Anthony Towns and Nikola Jokic.
“I think he’s the best perimeter defender in the NBA for multiple reasons,” Simplis said. “He’s able to guard one through five.”
Simplis also argued that Castle deserved All-Defensive recognition in his second season, although the 21-year-old did not make either team. His focus this summer has instead shifted heavily toward shooting consistency and conditioning.
Castle shot 47.1% from the field and 33.2% from three during the regular season, improving from 42.8% and 28.5%, respectively, as a rookie. Simplis said Castle made meaningful progress during the second half of the season and wants him to carry more consistent shooting mechanics into 2026-27.
The offseason program has included a 625-shot workout designed to limit consecutive misses, with 500 initial attempts followed by 125 off-the-dribble shots. Simplis said Castle went through his first 150 attempts in one recent session without missing two consecutive shots and with approximately 25 total misses.
Castle has also added weekly sand-dune running sessions in Manhattan Beach as part of his conditioning work. Simplis believes the additional training can help Castle sustain his defensive and offensive responsibilities over a longer season.
The Spurs will again have several ball-handlers around Castle, including De’Aaron Fox and Dylan Harper, making off-ball development another priority. Simplis said Castle has worked on catch-and-shoot opportunities, attacking closeouts and creating from secondary actions.
After averaging 7.4 assists per game and posting 18.2 points per game during San Antonio’s run to the Finals, Castle enters his third season with a larger statistical foundation and a more demanding role to build upon. Simplis believes the next step is turning those gains into sustained production at both ends of the floor.
