San Antonio Spurs guard Stephon Castle has established himself as the premier perimeter defender in the NBA, according to his personal trainer Olin Simplis. Entering his third professional season, the 21-year-old combines elite physical traits, relentless defensive versatility, and a grueling summer training regimen designed to elevate his offensive consistency following a deep postseason run.
The Defensive Anchor of San Antonio
During the 2025–26 NBA season, Castle proved to be a cornerstone of the Spurs’ defensive identity. Standing 1.98 meters and weighing 98 kilograms, the versatile guard logged averages of 16.7 points, 7.4 assists, and 5.3 rebounds across 68 regular-season games. San Antonio finished the campaign with a 62–20 record, advancing to the NBA Finals before falling to the New York Knicks in a five-game series.
According to Simplis, Castle’s defensive workload is unlike almost anyone else’s in the league. Speaking to R.org, the trainer highlighted the guard’s rare ability to shoulder extreme responsibilities on that end of the floor. «Onestamente penso che sia il miglior difensore perimetrale della lega», Simplis stated, emphasizing Castle’s unique capability to guard every position from point guard to center. Throughout the season, Castle drew assignments against premier playmakers and scorers such as Shai Gilgeous-Alexander and Anthony Edwards, while also battling formidable frontcourt stars like Julius Randle, Karl-Anthony Towns, and Nikola Jokic.
Postseason Production and Fatigue Management
Despite logging heavy minutes—averaging 33.0 per contest across 23 playoff games—Castle raised his production when it mattered most, posting 18.2 points, 6.1 assists, and 5.0 rebounds per night. Yet, the grueling nature of guarding opposing team’s primary options took a physical toll. In the Finals series against the Knicks, Castle dipped to 37.7% shooting from the field and 30% from beyond the arc. Simplis pointed directly to his multi-positional defensive assignments as the primary driver behind those shooting struggles, noting that guarding everyone from elite perimeter creators to power forwards and centers leaves very little left in the tank for offensive execution.
Statistics from the regular season showed clear overall progress, nonetheless. Castle improved his shooting splits to 47.1% from the field and 33.2% from three-point range, a significant jump from his 42.8% and 28.5% marks during his Rookie of the Year campaign. Despite those strides, Simplis argued that Castle deserved an NBA All-Defensive team selection for his second-year performance, an accolade he ultimately missed out on.
Rigorous Offseason Adjustments
To prepare for an even more demanding 2026–27 schedule—which will feature De’Aaron Fox and developing guard Dylan Harper—Castle’s offseason work with Simplis has focused heavily on shooting mechanics and physical conditioning. Because deep playoff runs shorten the traditional summer window, their program began with a deliberate, low-intensity buildup to avoid injury risks.
The core of their shooting drills centers on maintaining proper energy transfer from the ground up, even when fatigue sets in. Simplis explained that when guards tire, their movement sequence often slows down just enough for the ball to reach the shooting pocket after their legs have already fully extended. To combat this, their workouts emphasize keeping the ball in the shot-line pocket while Castle’s hips remain bent in a crouch position.
As part of his conditioning and accuracy training, Castle resumed his demanding “500 drill,” expanding the regimen into a 625-shot routine that requires him to take 500 initial shots followed by 125 off-the-dribble attempts while minimizing consecutive misses. In a recent session, he completed his first 150 attempts without missing twice in a row, totaling roughly 25 misses overall. This gym work is paired with weekly conditioning runs up the sand dunes of Manhattan Beach to sustain his high-volume, two-way role.
Next Steps for the Spurs
With San Antonio rounding out a competitive roster, Castle faces a tactical shift heading into his third year. The addition of Fox and the progression of Harper mean Castle will frequently operate off the ball, requiring refined catch-and-shoot abilities, aggressive attacks on closeouts, and secondary playmaking. Simplis noted that the ultimate objective is translating these mechanical adjustments and physical foundations into steady, nightly production on both ends of the floor.
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