Welcome to Player Attack!
"Qualified and experienced" members of the Counter-Strike: Global Offensive community will be named as "Investigators", and given the fun job of reviewing reports of disruptive behaviour. An active Overwatch button will appear on the CS:GO main menu - clicking it will present the Investigator with a pending case to evaluate. Each replay will be around 10 minutes in length (eight rounds), and the Investigator must determine whether the report is valid, consider the severity of the offense, and then apply a temporary ban if and when appropriate.
Possible verdicts include "Majorly Disruptive (cheating", "Minorly Disruptive (griefing)", and "Insufficient Evidence".
Privacy is protected - the suspect is referred to only as "The Suspect", and all other players' names are replaced. All text and voice chat is omitted, so the Investigator can judge each case solely on the in-game actions.
The Overwatch FAQ addresses the important question: How can you become an Investigator?
Investigators are selected based on their CS:GO activity (competitive wins, account age, hours played, Skill Group, low report count, etc.) and, if applicable, prior Overwatch participation level and score (a function of their accuracy as an investigator). Community members who maintain both a high level of activity and a high Overwatch score will receive more cases to elect to participate in.
...while the system's in beta, Overwatch will issue fewer cases for judgement, and each case will still be reviewed by Valve before any bans are applied.