Sherrill has a new slider.  The sweeping kind. I noticed this at the beginning of this year, but didn't mention it at the time because I wasn't sure if he used two sliders or something else was going on. Mid-way through the year Sherrill's slider movement indicate that he's using something entirely different from last year.

Full-breakdown after the break:

So how exactly has his slider changed?

According to Fangraphs the slider's vertical movement has changed from 1.4 to -1.5 a change of approximately two more inches down.  One inch might be pitch fx equipment error but 2? Now to check the horizontal movement. It was at -4.5 last year and -3.6 the year before. It now sits at -7.3 almost double the movement.

In order to create this much more movement slider velocity has to drop. It drops by ~2-3 mph while the rest of his pitches stay pretty steady edging up slightly in some cases with the exception of his curve (this pitch too has more movement with a similar ~2-3 drop in mph).  Sherrill has made a conscious decision to sacrifice speed for much more movement.

So has this new pitch been effective? The linear weights show that his slider has improved from -0.15 runs above average per 100 pitches to 1.35 runs above average per 100 pitches. His slider in total has been worth 2.1 runs above average, much better than the -0.3 he had last year. 

Part of this gain is probably due to better set-up of the slider as his fastball has increased ~half a run above average per 100 pitches. More likely the increased success of both pitches has allowed both pitches to become much more effective.

The new sweeping slider with more movement has contributed to Sherrill's 0.9 WAR in just over half a year compared to his 0.4 WAR for all of last year