Pre load entity reference fields into a node Say I have three content types: Team member, Team and Matchday. 

The team content type is made up of entity reference fields, which reference team members. 

The Matchday content type should load team members from the Team content type automatically each time a new piece of content is created. Then the content editor should be able to delete people on each Matchday who don't show up, and also add members from other teams who are filling in. 

Anyone know how to do this in Drupal 8, even just a general idea to point me in the right direction?
Add an entity reference field to team members content type.
Using form alter:
Hide the above field in the add form.
Add an entity reference render element that points to the team content type.
In the submit callback load all the team members that in the selected team and add them to the entity member field.