When the calender turns to September and teams prepare for the mad dash to the finish line, they are allowed to expand their active rosters from 25 players to a maximum of 40 players. While it offers teams without playoff hopes an opportunity to showcase or test interesting talents and top prospects in the major leagues for a short time, contending teams use the additional roster space to fill holes in their lineup and to bolster their depth. Whether it is adding a defensive specialist or a player who excels against left handed pitching, contending teams look to gain any advantage.
One area that every contending team seeks to improve or deepen during this time period is the bullpen. The help arrives in a variety of ways; David Price was a top prospect who gave the 2008 Rays a late innings option while less heralded relievers can absorb worthless innings, conserving the better arms in the bullpen.
For this reason, bullpens should, in theory, improve during the final month or so of the baseball season. Managers have more options as well as better rested arms at their disposal. But have the bullpens actually improved?
From 2008-2012, major league bullpens posted a 3.90 ERA and a 4.01 FIP during the regular season. As fall crept up and the season transitioned into September, teams posted a 3.90 ERA and a 3.93 FIP. While there is a slight difference in the FIPs, it is small enough to write off, especially considering the ERAs are exactly the same.
However, these stats account for all teams, including those awarding auditions to players in games that don't particularly matter for them. How have competitive teams' bullpens fared in the months of September and October (regular season games only) compared to the full season?
Competitive teams are defined as all teams, in both leagues, that finished within 3 games or less of a playoff position. From 2010-2012, 33 teams fit this grouping.
During the 2010-2012 seasons, the "competitive" teams had a collective 3.43 ERA and 3.70 FIP in relief. Interestingly enough, during September and October and with the additions of call-ups affecting their performance, the bullpens pitched to a 3.37 ERA and a 3.73 FIP. All this evidence suggests that the additions of more relievers didn't actually help the bullpens, producing no noticeable effect.
I have two initial theories for this. With the expansion of rosters inclusive to both hitters and pitchers, any positive effect from bringing in situational relievers is negated by the addition of situational hitters. The late innings of a close September game can become a mess, with hitters and pitchers frequently being replaced as opposing managers try to attain the upper hand.
Another possible cause for the lack of improvement is that many of the pitchers called up have to adjust to the major leagues. While seasoned veterans should have no issue re-acclimating themselves to the major leagues, teams often try using top starting pitching prospects in the bullpen for the first time. While some have no issue making the adjustment (David Price), others struggle with the quick and short change (Jeremy Hellickson and Matt Moore).
Out of curiosity, I decided to see how the Rays do at utilizing reliever call-ups in September. Is there no effect, as is the case for the league, or have the Rays managed to excel in this area?
From 2010-2012, the Rays called up nine different relievers for September. Notable names include Jake McGee, Alex Torres, Brandon Gomes, and Dane De La Rosa. Altogether, they pitched 45.1 innings with a 3.97 ERA and a 3.71 FIP.
During the regular season (from 2010-2012), Rays' relievers pitched to a 3.29 ERA and a 3.67 FIP. In September and October (excluding the postseason), the relievers posted a 3.31 ERA and a 3.70 FIP. So though the Rays actual call-ups pitched moderately worse than the regulars, there was no significant overall effect.
So though we may all get excited about the addition of some new arms to the bullpen in September, the reality is that there is little evidence these pitchers do anything to improve the bullpen. It may excite us to see new and unfamiliar faces try to make their mark, but the overall impression is insignificant.