I would have preferred Castillo with Bannister in mind - without letting onto that, I posed Gemini with a choice between Banny working with Peralta or Castillo and thought its output was insightful for once: From a White Sox perspective—especially with Brian Bannister leading executive pitching development—you take Luis Castillo over Freddy Peralta. Both pitchers possess elite ceiling, but when evaluating a stretch-run rotation arm through the specific lens of Bannister's pitching philosophy, Castillo provides the ideal clay to mold. 1. The Brian Bannister Factor: Mechanics & Pitch Profiles Bannister’s methodology revolves heavily around biomechanics, seam-shifted wake, optimized tunnel design, and pitch-design leverage. Luis Castillo (The Moldable Ace): Castillo possesses world-class, unteachable raw traits: elite fastball velocity (touching upper 90s) and a dynamic changeup with elite fading action. However, Castillo occasionally struggles when his fastball shape flattens out in the upper zone or when his slider usage gets inconsistent. Bannister excels at refining fastballs to maximize vertical ride or lateral movement, optimizing high-velocity pitchers so their secondary stuff plays up. Freddy Peralta (The Cross-Body Outlier): Peralta’s effectiveness relies heavily on his unique, highly deceptive cross-body delivery and low release height, which creates an unusual approach angle for his fastball. Because Peralta’s profile is tied so intricately to a non-standard delivery, altering his mechanics or pitch shapes carries a higher risk of disrupting his deceptive arm path. 2. Postseason Rotation Longevity & Inning Volume For a high-stakes postseason push, you need a starter who can consistently carry deep workloads without compromising stuff. Castillo's Durability: Castillo has a proven track record as a frontline workhorse. He routinely logs deep starts, handles 100+ pitch counts comfortably, and holds his velocity late into games—a critical trait for minimizing postseason bullpen strain. Peralta's Workload & Command Variance: While Peralta can deliver dominant, high-strikeout outings, his pitch counts tend to escalate quickly due to walks and deep counts. In a playoff environment where every base runner is amplified, a pitcher who averages under six innings per start puts excess pressure on the rest of the pitching staff. 3. Batted-Ball Profile in Playoff Environments Castillo: Generates a healthy mix of swing-and-miss while maintaining solid groundball rates when pairing his two-seamer and four-seamer. This gives him multiple paths to escape high-leverage jams (e.g., inducing a double play). Peralta: Relies heavily on fly balls and high pop-up rates. While pop-ups are valuable, high fly-ball rates carry inherently more variance—particularly in warm weather conditions or against modern, power-heavy playoff lineups. The Verdict Luis Castillo is the choice. His physical baseline, elite raw pitch velocity, and durable frame make him the exact type of power starter that Bannister’s pitch-design framework can maximize into a postseason ace.