From Jeremy Greenhouse:
It’s the manager’s job to get the most out of his players. With regards to the bullpen, this means optimally inserting relievers depending on such factors as the current baserunners, batter, and score. Hence, relief contributions tend to be measured by Win Probability Added. Having a bullpen ace makes the managers job easier in that he doesn’t even have to think about whom to give his highest-leveraged innings. LOOGYs are always nice too. FanGraphs has a statistic that compares a player’s WPA in high-leverage situations vs. his WPA in low-leverage situations, to see how relatively Clutch that player is. Looking at the bullpen as a collective unit, we can more or less make the assumption that a Clutch bullpen has been managed well, which is to say that better relievers are pitching in well-deserved, higher-leveraged innings.
Click through to read the rest of the article, where you will find that the “clutchiest” bullpen in baseball this season has been that of the Yankees. As I have said on many occasions, while we may quibble with some of the individual moves made by Joe Girardi, he has done a very good job keeping the big picture in mind when making his bullpen moves. This has allowed him to leave important spots for his best pitchers without overworking any of them.
(Just as a point of comparison, Joe Torre’s Dodgers grade out as one of the worst clubs in this regard, despite having a large number of very good relievers.)