A bit more info on how to achieve this (using shawnrosspeters example) with Post-2-Post without any code tweaking:
With ACF Post-2-Post, this can be done simply by:
Team CPT
– Create a custom field group for Team CPT
– Set the field group to be visible only on Team CPT
– Create there the field “Related Players” and give it the fieldname “players-teams”
– Filter by Post Type = Player CPT
Player CPT
– Create a custom field group for Player CPT
– Set the field group to be visible only on Player CPT
– Create field “Related Teams”
– Reuse the same fieldname as for Team CPT Related Players (“players-teams”)
– Filter by Post Type = Team CPT
* With this method, you will have a different field label for each of the 2 different custom post types.
* The filtering will only to show results of the other CPT when selecting posts for the relationships.
* By virtue of using the same fieldname “players-teams” in both field group fields, the Post-2-Post plugin works perfectly, ensuring that the bidirectional relationships are established.