Yesterday, while in a party of four, we chose to test out Captain's Mode – we made the person who wanted to draft and pick leader of the party.
When the game started though, the 5th member of our team, which was not in our party became the captain.
He didnt write a single line in chat and didnt respond to us and we ended up with heros that we didnt want to play and had an unwinnable lineup (KotL, PA, Tree, Weaver, Puck vs Magnus, Enigma, Gyro, Nyx and Lina).
After this horrible game, we decided to never play Captains Mode again unless we are 5 people.
But I'm still wondering if there is any insight on how the Captain is chosen, and if we did something wrong when queuing up if we wanted one of our players to draft.
Best Answer
EDIT: Ever since the First Blood update, the behavior below is no longer applicable. Now captains are no longer randomly assigned. Instead, there is a button to allow anyone to make themselves the captain, first-clicked-first-served.
== OLD ANSWER ==
It is random based on the number of groups. What that means is, by grouping up as 4 and taking on one straggler, your group/captain has a 50% chance of being the drafter, and the solo guy has 50%. If you were to group as 3 and take on two other solos, it would be 33/33/33, whereas if you caught a pair of partied players with your trio, it would be back to 50/50. A pair and three solos would make 25/25/25/25, and so on...
Long story short, unless you can live with this quirk in the CM system, I do suggest getting a fifth in your stack. Otherwise, give Random Draft a try. It can be just as strategically interesting as CM.