25 games is the requirement to add position elegibility:
Section A- Determining Eligibility
Item AVIII A-1.0 Eligibility
Players are always eligible for at least one position.
To gain position eligibility a player must have played 25 GP or 20 IP played at the position within a particular season (This represents half of the eligibility for prospect contracts)
Current and past season statistics are used to determine eligibility.