Don't worry everyone, it's very simple. I'm sure Old Red and others will find it very clear...
Calculation:
To determine if a pitcher has earned a Shutdown or Meltdown, you simply need to check their Win Probability Added (WPA) for the game in question. WPA is a measure of how much the team’s Win Expectancy changed while a given pitcher was on the mound. If you enter a game with a WE of 84% and exit the game with a WE of 94%, the pitcher is credited with +0.10 WPA. If you enter with a WE of 64% and leave with a WE of 46%, the pitcher earns -0.18 WPA.
In order to delineate between outings of consequence and those without much, relievers only earn Shutdowns if they register a WPA of +0.06 or greater in a given game. The same is true on the negative side of the ledger, earning a Meltdown if they produce a -0.06 WPA or lower during a game.
Keep in mind that Win Expectancy is based on the odds an average team would win on average, so if the 2001 Mariners were playing the 2003 Tigers, WE would treat a 4-0 game in the 9th the same as if two very equal teams were in the same situation. Additionally, a WPA of 0.40 and 0.08 both earn a Shutdown, even though the former is very likely a more impressive performance.