What is the List or Play Rule in Sorare: MLB?

Managers who include a card in a Sorare: MLB lineup will not be able to simultaneously list it on the Manager Sales Market for sale or include in a trade offer (i.e. Managers cannot list and play cards at the same time).

This only applies to Managers who initiate sales or trades, not those who receive offers – if or when they accept. Once a sale or trade transaction is complete, the related card(s) are immediately invalidated from current lineups. 

For example, if a Manager lists a card on the Market, it cannot be entered in a lineup unless the Manager acknowledges the card will be delisted, or removed, on the Market. To list a card on the Market – for sale or to include in a trade – Managers need to confirm the listing and acknowledge it will remove the player card from lineups (both live and upcoming). Managers will receive a warning prompt that listing a card on the Market will invalidate their lineup, and vice-versa.

Please note this list-or-play rule applies to all sports.