Blizzard has implemented a new penalty to punish rage quitters who bail early on matches in the new shooter, Overwatch. According to the game's community manager, once a player's games played vs games completed falls below the required threshold, a warning message will be sent.
Disconnects are calculated based on the player's 20 most recent games. Should the player continue to leave games after the warning is handed out, this will be deemed as rage quitting and a 75% EXP penalty will be applied on all future games.
This means that it's not an instant penalty, but players must be careful if they're prone to leaving games part way through. However, should a player disconnect or get kicked due to inactivity, it will still be counted as if it were done intentionally. Here's an explanation:
If you leave a game before the "Assemble Your Team" phase is over (i.e. before you enter your starting spawn rooms):
It won't count as a game played
You will not be considered a "leaver" in this scenario
If you leave a game after the match ends (i.e. after you see the VICTORY/DEFEAT screen):
It will count as a game played—and if your team won, it will count as a win
You will not be considered a "leaver" in this scenario
If you leave a game after the "Assemble Your Team" phase is over, but before the match ends:
It will count as a game played
You will be considered a "leaver" in this scenario
The basic rule is don't rage quit, and help ensure that the team-based game stays as fair as possible. Blizzard goes into more detail in their forum post if you want to know more.