It is now possible to create a subgroup directly from the draft of an event.

You can select one of these lists - all, Going, Not going and then click on the three dots on the right and select "Create subgroup".

Then the window opens where subgroups are created with pre-filled members who were on the list, e.g. if the coach selects the "Attendance" list, everyone who is registered for the event will join the group.