Players can only accumulate pitching statistics or hitting statistics in a given Game Week, not both.
For example, Shohei Ohtani is capable of both pitching and hitting. Sorare: MLB players will need to decide whether to count Ohtani's pitching OR hitting statistics during a given Game Week. This means he can only be played specifically as a Starting Pitcher (for pitching statistics), Corner Infielder, or Extra Hitter (for hitting statistics).
As a result, Shohei Ohtani cannot be selected for the Flex position.