Heroes of the Storm Wiki
The Unranked Draft screen.

Unranked Draft is a gameplay mode of Heroes of the Storm. Unranked Draft mode allows up to five players to queue together in a Hero League-esque drafting format: Teams alternately pick heroes, without any duplicates allowed. A coin flip decides which team goes first.

Unlike Hero League, there are no restrictions on player or Hero levels, so basically anyone can play. This (somewhat) removes the randomness of compositions by allowing teams to coordinate their picks and put together a coherent composition. They can also ban out some of the stronger Heroes they don't want to play against. It's like Hero League without the pressure of ranking up or down—stress-free, casual, but not random.

Players entering Unranked Draft Mode for the first time will use their Quick Match Matchmaking Rating as a guideline to determine initial matchmaking. After that, the system will use Unranked Draft instead of Quick Match MMR as the guideline to determine a player's matches.[1]

Players who repeatedly leave will be flagged to receive leaver penalties. Players with active penalties for leaving games can no longer queue for games.