To call any of Mariano Rivera’s seasons elite seems kind of pointless. I don’t think anyone would argue that he is definitively the greatest relief pitcher of all time. He currently has the 16th most Pitching Runs ever, despite having only the 805th most innings accumulated. His 205 ERA+ is the greatest in MLB history. He had stretch where in 8 of 9 seasons he had an ERA below 2. There is a reason that he was the focal point of this years All Star Game. Nobody has been able to do what Mo has done. When you add in his postseason credentials it’s a slam dunk Hall of Fame case, something rarely, if ever, said about a relief pitcher. However, I feel there is one season that stands out among the rest. In 2008, at the ripe old age of 38, Mariano may have put together the best year of his career.
Lets start off with the obvious, in 2008 Mariano had a 1.40 ERA. Remarkably that is not even the lowest total of his career. In 2005 he had a 1.38 ERA. However, he did have a career high 316 ERA+ in 2008. He is the only player all time to have 2 seasons with at least 60 innings, and ERA+ of 300 or better. I know in many ways single season ERA is not a great way to evaluate relievers. This was not a mirage ERA, hiding behind poor peripherals. He had a FIP of 2.03, and xFIP of 2.28 in 2008. The 2.28 xFIP is the greatest of his career(data only goes back to 2002).
The way he amassed such a low xFIP is by completely eliminating walks. He walked a career best 2.3% of batters. His 0.76 BB/9 is the 10th best since 1950 among pitchers with at least 60 innings pitched. He in no way had to cut down on his strikeouts in order to reduce his walks. His 29.7% strikeout rate was his best since 1996 when he had a 30.6% K rate. This added up to a 12.83 K:BB rate. He has never had another season with at least an 8 K:BB rate. The 12.83 ratio is the 2nd best in history(minimum 60 innings), only trailing Dennis Eckersly’s incredible 18.25 K:BB season in 1990. As an interesting side note, Dennis Eckersly did not have a single walk during the 48 appearances in which he earned a save that year.
Alright, back to Mariano. In 2008 he was not just good at the things included in FIP, but was also excellent at hit prevention. I am well aware that a low BABIP usually indicates that a pitcher was lucky. On the other hand studies have been done showing that relievers do have an ability to reduce quality contact, notably by Dave Studeman of The Hardball Times. This is especially true for pitches with movement, like say a cutter. In 2008 Mariano opponents had a .218 BABIP. Combine that with a high strikeout rate, and a good ability to prevent homeruns(only 0.5/9), and they accumulated a .165 batting average against him. With that low batting average, and a historic walk rate, opponents had a .190 on-base percentage against him. That is the 4th best since 1945, the first year that baseball reference has opponents batting statistics. It’s not like he was allowing many extra-base hits. Opponents only had 9 extra-base hits in 249 at-bats. That led to a .233 slugging percentage, and a personal best .423 OPS. The .423 OPS is the 7th best of all time.
Looking at the Fangraphs pitch data shows that his cutter was particularly nasty that year. His 24.9 runs saved on it that year were a career high. We may never see a better pitch than his cutter. He literally built a Hall of Fame career on it. There are many great young relievers in baseball right now. Craig Kimbrel is making a batters look foolish on a nightly basis. Aroldis Chapman is blowing 100+ MPH heaters past guys. Kenley Jansen is quickley becoming a star, and just finished up a hidden perfect game. With all the fascinating up and comers closing for playoff contenders it can be easy to ignore that Rivera is back to his old ways. Don’t forget to make sure you watch him over this last month, because there will never be another Sandman.
