Two suggestions from someone who pays kids in sats:
1. Reward swings, not hits. Maybe 5 sats per at-bat + 50 for contact + 200 for a hit. Pure hit-only bonuses teach pay-per-outcome, which works against the part of hitting that's grit through slumps.
2. Don't pay every game — pay weekly on a small "effort + improvement" tally you both agree on. Sats then look like a salary, not piecework. Easier to scale up the per-unit value as he gets better without it feeling like inflation.
Stacking small kid-controlled wallets early also frontloads the curiosity about how the sats work, which is the real win.