The brawler/battle arena genre seems to attract an inordinate amount of poor behavior, perhaps a result of the highly-competitive environment. Heroes of the Storm isn't an exception, even in the game's alpha phase. Fortunately, Blizzard isn't willing to let such behavior slide. According to a post made by Community Manager Vaeflare, players "who have been found to be repeatedly AFKing, leaving games, or determined to be toxic" will be banned from Heroes of the Storm.
While AFKing through matches is bad enough as it is, we find it particularly absurd that some players are choosing to AFK in a game's alpha, where participation means testing the game's mechanics. The only thing you're testing by going AFK is how quickly Blizzard will remove you from participation.
Vaeflare's full post can be found below or on Battle.net.