Coming into the season, Royals fans were fed the line that the team wanted to build one of the best bullpens in the league (as opposed to the teams who want their bullpens to be terrible). The logic behind this company motto was that the bullpen could help pick up the slack from the starting rotation, which is why they needed to sign Jonathon Broxton to a four million dollar contract this off-season.
To the Royals credit, the bullpen does lead the league in fWAR this season, at 6.9. Part of the Royals high WAR total is due to the fact the bullpen has thrown the third most innings out of any bullpen in baseball this season, but it does need to be noted that the Royals bullpen has been effective when called on.
The good news for the Royals is that they have four quality relievers who are young and cost-controlled, so the bullpen should continue to be effective in the future. Greg Holland, Kelvin Herrera, Tim Collins and Aaron Crow have all pitched well out of the bullpen this season, and their peripheral statistics support their low earned run numbers.
Fangraphs has Holland as one the five most valuable relievers this season, with Herrera as a one of the top ten most valuable relievers. Crow and Collins are both around the 1.0 WAR mark for fWAR and rWAR, which is a strong number for any reliever.
Holland and Collins have similar strikeout-to-walk numbers. Both Holland and Collins are striking out an absurd number of hitters (greater than 12 per nine, for those who are not used to percentages), but are walking more hitters than one would like (four per nine). Both relievers throw a lot of pitches outside of the strike zone in an attempt to get batters to chase and strikeout, so the walk rate is probably tied in with the strikeout rate. The difference in FIP between the two pitchers is due to Collins tendency this season to surrender the longball, while Holland has kept the ball in the park well for two consecutive seasons.
Crow and Herrera's peripheral numbers are similar as well, with Herrera's numbers being slightly better in both categories. Herrera has been truly dominant this season, as he sports a 55.4% ground ball percentage to compliment his strong strikeout-to-walk numbers. Crow has improved this season compared to last, despite a lower ERA and an All-Star appearance in 2011. Crow's walk numbers last season were similar to Collins and Holland's this season without the absurdly high strikeout numbers to offset the walks. His HR/FB percentage has halved from last season, something all Royals fans should hope will continue.
The Royals have done a good job laying the foundation for a high-quality bullpen for the next few seasons, and deserve credit for acquiring these arms. Even though the Royals have had one of the best bullpens in the league, however, the team has not been close to contention this season. Although a team's bullpen is important to it's success, it should be clear after watching this Royals team this season that starting pitchers and position players are much more important to a team's success due to the increased opportunities regular players have to affect the game.
If Dayton Moore uses some the of David Glass is claiming he will spend this off-season on another Broxton, the money will be wasted. The Royals bullpen should already be a strength, adding a high-priced reliever will be a waste of resources that should be spent shoring up areas of weakness. Their are plenty of arms already in the system that can compete next spring to fill in the final two or three spots in the bullpen (without factoring in Joakim Soria, who deserves his own post), so depth should not be an issue. Moore has assembled a young, quality bullpen; now he needs to make sure he takes advantage of it.