San Francisco Giants

Sergio Romo’s declining slider

Sergio Romo San Francisco Giants 2014 Spring Training

Sergio Romo doesn’t have a typical Major League pitcher’s body. He doesn’t have a mid-90s fastball. He doesn’t even have a 90 mph fastball. What he does have is a slider that’s the envy of pitchers everywhere. He has made his living based on this one pitch and its ability to make the best hitters on the planet look like this.

During his best seasons (2010-13), Romo’s slider was one of the best in all of baseball, and he threw it 51.4% of the time. Even though hitters knew it was coming it was a nearly unhittable pitch, ranking as the most valuable slider among relievers.

This year he has thrown the slider a bit less, just 49.5% of the time, but the results have been drastically different. The Romo slider that was the best in baseball over the last four seasons has slipped down to 89th this season.

The slider  hasn’t looked all that different to the naked eye, but this season there has been a measurable loss of movement in the pitch. During his peak from 2010 to 2012 his slider had 9.5 inches of horizontal movement — that put him at the extreme end and made his slider truly special. This season, Romo’s “no-dot slider” has averaged just 8.2 inches of horizontal movement, putting it into just very good status.

It probably isn’t a coincidence that this loss of movement has happened at the same time that he has generated less swings and misses with his slider.


From 2010 to 2012 his slider generated a whiff on nearly half of all swings. Batters have swung and missed only a little more than a third of the time in 2014

The other bad trend is seen in the results when contact is made. From 2010-12 his slider produced a .152 batting average and .255 slugging percentage against. So far this year the slider has produced a .221 batting average and .481 slugging percentage.

Fewer swings and misses result in fewer strikes. Fewer strikes leads to fewer strike outs (his strike out rate is 22.9% the lowest of his career) and more balls. More balls leads to more walks (his walk rate is 5.9% the highest since his rookie season) and more favorable hitters’ counts. Getting behind in the count results in a lower margin for error and more mistake pitches that have been hit hard (his HR/9 of 1.9 is more than double his previous worst mark).

Romo’s bad season thus far doesn’t seem to be a small sample problem or just a few bad pitches turning into home runs. The trend over the last few seasons shows that we have probably seen the last of Sergio Romo as a dominant relief pitcher. He should still have a role in the Giants bullpen this season, but it looks like his time as the top option for Bruce Bochy has come to an end.

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