Don't Trust a Reliever Farther Than You Can Throw Him

Relievers have been in high demand this offseason. Potential closer candidate Andrew Miller received a four-year deal for $36 million while David Robertson received four years and $46 million. Non-closers like Pat Neshek received two years and $12.5 million while Luke Gregerson got three years and $18.5 million. The value of a good bullpen was proven when the Royals rode their top guys to the World Series last season. But many believe that even the best relievers can be highly volatile and therefore teams should be skeptical of offering them large contracts. In order to see whether this is valid, I looked at all of the 301 relievers from 2010-2012 who threw at least 50 innings in relief during that stretch, and compared their performance for 2013 and 2014 to all 265 relievers who threw at least 40 innings in relief using ERA, WAR, and RA9_WAR.

The chart below shows how each of the top 50 relievers according to each of the statistics from 2010 to 2012 performed in 2013 and 2014. 

Only 31.5% of the top 20 relievers and 24.1% of relievers ranked 21-50 according to ERA in 2010-2012 were top 50 relievers in 2013 and 2014. The average top 50 reliever ended up being an asset to the bullpen but wasn’t the star reliever that the team signing him was hoping to receive. The average ERA of roughly 3.15 looks like it's acceptable. However, 100 out of the 265 relievers who threw at least 40 innings in relief from 2013 to 2014 had an ERA under 3.00. An ERA of 3.15 is slightly better than the median ERA of 3.35 for all qualified relievers.

45% of the top 20 relievers and 17.2% of relievers ranked 21-50 according to WAR in 2010-2012 were top 50 relievers in 2013 and 2014. The value of their contributions decreased dramatically from 2010-2012 to 2013 and 2014.

25% of the top 20 relievers and 36.7% of relievers ranked 21-50 according to RA9_WAR in 2010-2012 were top 50 relievers in 2013 and 2014. A number of top relievers according to RA9_WAR from 2010 to 2012 such as Sean Marshall, Jonny Venters, Jason Motte, Eric O’Flaherty, Jesse Crain, Rafael Betancourt, and Joel Hanrahan suffered injuries in 2013 or 2014 that significantly impacted their value. It is questionable whether the large amount of injuries for relievers ranked in the top 20 in this category is typical.

In addition, success rates weren’t impressive when using multiple measures to determine reliever quality. The five relievers ranked in the top 20 using each measure were Craig Kimbrel, Mariano Rivera, Sergio Romo, Mike Adams, and Darren Oliver. Kimbrel has remained excellent and is easily a top five reliever while Rivera retired after 2013, but Romo, Adams, and Oliver were all disappointments. Likewise, there were nine relievers ranked in the top 20 of two of the categories and in the top 50 in the other category. Four of those nine relievers ended up getting hurt and unsurprisingly only four of the relievers in that category were actually successful. Of the nine relievers who were ranked in the top 20 of two of the metrics without being ranked in the third, the only successful ones were Tyler Clippard and Joaquin Benoit.

The problem is that elite relievers have very little room for error. The top relievers had an ERA of about 2.00. If they throw 63 innings a season, then that means they can only allow 14 runs. If they end up allowing just eight more runs per season, then their ERA is closer to 3.14 and they are simply average. The difference between the best relievers and decent relievers is minuscule and can come down to a few good or bad breaks. At the same time those same extra seven runs are more important than the average run because elite relievers are usually used in the most crucial situations.

Some top relievers from 2010 to 2012 were still good in 2013 and 2014. But on the whole a top reliever from 2010-2012 was unlikely to be elite in 2013 and 2014. It doesn’t make sense to pay relievers for past performance because it isn’t likely that they will be able to repeat it. A team that has limited amounts of money should focus on either position players or starting pitching. Quality relief pitching is important, but there are so many variables involved that are outside the pitchers' control that even the best relievers can't consistently provide it.