Reliever Pitching Metric Correlations, Year-to-Year | FanGraphs Baseball

It makes perfect sense. Starters having more pitches to fall back on. Relievers usually only have one or two good pitches, so the pitcher has less options to make adjustments.

This lines up well with what Jeff Zimmerman and I found regarding pitcher aging and how it differs depending on a pitchers role.

Let’s take the example of strike outs. Jeff and I found that while starting pitchers were able to mitigate against their decline in velocity–and therefore experienced a less drastic decline in their strike out rate–relievers were far more dependent on their velocity. As a result, relievers generally were more likely to see sharper declines in strike out rates from year to year.