#Ecto.Changeset<
  action: :insert,
  changes: %{
    pitch_players: [
      #Ecto.Changeset<
        action: :insert,
        changes: %{shirt_number: 66},
        errors: [name: {"can't be blank", [validation: :required]}],
        data: #Lineup.Player<>,
        valid?: false
      >
    ]
  },
  errors: [],
  data: #Lineup<>,
  valid?: false
 >