Hi Matt! Welcome. If looking for workout guidance for pitchers, follow Eric Cressey on twitter. For my son, also a youth pitcher, I got him the https://highperformancehandbook.com/ and he has been following the workout for about a year and a half. Included are workouts, nutrition, videos of his specific exercises. He is big into shoulder and arm health.
Nothing wrong with sprinting. Focus on the start. Here is a drill. Go to a football field. Think of 100 yds as an inning. Do ten 10 yd sprints to cover the football field. Rest about 30 seconds between each 10 yd sprint. Start from a sprinter's crouch position. Really focus on the explosion off the line for each sprint. After you do ten, 10 yd sprints to cover the field, rest a few minutes. You just pitched inning #1. Alternate which leg you start your sprint with each time. Go ahead and get a few innings in. Maybe extend on inning to 20 sprints. You can take a break if form is breaking down. Pretend it's your coach coming to the mound to tell you "just throw strikes". LOL!
Good luck!