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Umps Not Buying Stephen Strasburg's Fastball

Stephen Strasburg and the Washington Nationals avoided arbitration on Friday, agreeing to pay the now 25-year-old right-hander $3.975 million next year according to CBS Sports' Jon Heyman. In terms of value, 2013 was Strasburg's best season -- posting 3.1 wins above replacement after generating a 3.00 ERA and 1.05 WHIP over 30 starts. These were modest improvements from his 2012 campaign, where he posted a 3.16 ERA and 1.16 WHIP over 28 starts before being infamously shut down by his club in the heat of a pennant race. Strasburg was worth 3.0 wins that season, so it's not out of the question to assume he would've been worth more had his season not come to a decidedly screeching halt.

Yet for as impressive as Strasburg's statistics have been to this juncture of his career, one cannot overlook the regression of his strikeouts -- which have been arguably the most dominant aspect of his game. Last season, Strasburg punched out opponents in 26.1% of their plate appearances against him, enough for the seventh-best mark among qualified starters. Two seasons ago, that number was an astounding 30.2%, which was the best among starters who tossed at least 150 innings. Dialing back the time machine even further, Strasburg's strikeout rate from 2010 (his rookie season) to 2011 (the year he was shut down after five starts) stood at 32% -- the sixth-highest mark in baseball among all pitchers with 90 innings during that span.

Why have Strasburg's strikeouts decreased 5.9% since his entrance into the league four years (yes, it's been four years already) ago? Advanced scouting reports and exposure to his stuff may have at least something to do with it, and there's that whole Tommy John surgery thing that may certainly play a role. But more than anything else, I think it's the fact that umps aren't favoring his fastball quite as much.

Comparing called-strike rates on Strasburg's fastball since 2010

stras2 on Make A Gif

Umps have progressively called fewer out-of-zone strikes on Strasburg's heater since his debut.

Strasburg's heater garnered a 13.7% called strike rate when located out of the zone over his 17 starts between 2010 to 2011. This was not a particularly lofty number, admittedly, as the league average mark was 12.2% over that span. But in 2012, that number decreased to 10% (lower than the 11.8% league average) and fell even further to 9.3% last season. Most of those called strikes have occured on the 'backdoor' portion of the plate to left-handed hitters or inside on righties, but as we see, that significantly decreased in frequency over the past two seasons.

What makes this decrease even more perplexing is that Strasburg's fastball velocity has decreased -- albeit minimally-- over the past three seasons, averaging 96.8 MPH in 2010-2011, 95.6 in 2012 and 95.3 in 2013. As my colleague David Golebiewski pointed out in his brillliant piece on Justin Verlander (if you haven't read it, you should), there tends to be an "inverse relationship between fastball velocity and called strike rate on out-of-zone fastballs -- the slower you throw, the more called strikes you get." Of course, this is more of a general statement and therefore isn't applicable in all cases, but we see that Strasburg is bucking the trend a bit in this respect, as his fastball velocity has decreased yet he is tabbing fewer out-of-zone called strikes.

What does it all mean?

Strasburg's progressive strikeout decrease has everything to do with him receiving fewer out-of-the-zone called strikes with his fastball. As the graph above shows, the fewer called strikes he receives with his heater, the less punchouts he is able to compile with it over time. Conversely, this has contributed to his increasing walk rate with the offering.

I've included a logarithmic projection for the first and second half of next season in the graph to get a sense for how (less) productive the pitch might be in the immediate future. Based off my findings, Strasburg fastball is on track to receive roughly an 8% out-of-zone called-strike rate by the end of next season, and could very well walk more batters (just over 10% in the projection) with the pitch than he strikes out (just under 10% according to the data). To put that into context? The league average starter's fastball generated a 15.9% strikeout rate and 8.4% walk rate last season.

Are umps not favoring Strasburg's fastball because it's lost some of the "flash" it showed during his 2010 campaign? We may never know. What I do know, however, is that this is concerning. A 25-year-old power arm once dubbed the best pitch prospect of his generation shouldn't see his strikeouts decreasing at this high of a rate.


Which Pitchers Pull a Glavine, Pull the String vs. Same-Handed Hitters?

It's one of the first baseball commandments that young pitchers learn: Thou Shalt Not Throw Changeups to Same-Handed Hitters. If you pull the string in such a situation, the thinking goes, you'll end up getting clobbered as batters turn on a pitch that flutters low and inside -- directly to their power zone. Most hurlers adhere to this teaching, lest they get burned for all eternity by their pitching coaches: lefty starters threw a changeup to lefties just 4.6 percent of the time in 2013, and righties tossed one to same-handed hitters 6.7 percent.

Newly-elected Hall of Famer Tom Glavine was a blasphemer, however, and a very successful one at that. During his last season in the majors in 2008, Glavine tossed a changeup to lefties a whopping 53.2 percent of the time. No other lefty came close, with Phillies Jamie Moyer (29 percent) and Cole Hamels (28.1 percent) ranking a distant second and third, respectively.

While Glavine struggled during his final year in the majors, he still managed to baffle lefties with his changeup. He induced more whiffs with his change (39 percent) than the league average (31 percent), and he also limited hard contact (.353 opponent slugging percentage, about 50 points better than the MLB average for lefty-on-lefty changeups).

Glavine excelled against lefties with his signature pitch by almost never locating low and inside. Instead, he pounded the outside corner. Against southpaw hitters, Glavine threw 78 percent of his changeups away:

Glavine's changeup location vs. lefty hitters, 2008 


Now that Glavine has reached Cooperstown by breaking the changeup commandment, it's worth asking: Which current starting pitchers share the Atlanta lefty's rebellious streak? As it turns out, a Tampa Bay righty has taken over Glavine's title as the game's biggest changeup iconoclast.

Jeremy Hellickson pulled the string 33.6 percent of the time versus same-handed batters last season, by far the highest clip among all qualified starters. Unlike Glavine, the man dubbed Hell Boy had no problem challening hitters inside with his changup:

Hellickson's changeup location vs. righties, 2013    


Among other righties, Ian Kennedy (20.1 percent), Kyle Kendrick (19.9 percent), Edinson Volquez (18.6 percent) and Kris Medlen (18.4 percent) also threw a bunch of changeups to same-handed batters. Medlen (.250 opponent slugging percentage) had the most success with righty-on-righty changeups out of this group, followed by Kennedy (.348) and Hellickson (.393). Volquez (.533) and Kendrick (.536), meanwhile, were smote by righties.

What about lefties? Mark Buehrle tossed the high rate of lefty-on-lefty changeups in 2013 (21 percent). Like Hellickson, Buehrle eschewed Glavine's approach by throwing plenty of low-and-inside changeups to lefties:

Buehrle's changeup location vs. lefties, 2013

Hamels (18.3 percent), Eric Stults (15.5 percent), Felix Doubront (9.1 percent) and Chris Sale (8.3 percent) pulled the string frequently versus lefties, too. Doubront (.185 opponent slugging percent) dominated batters, as did Stults (.189). Buehrle (.315), Hamels (.333) and Sale (.375) didn't get cut down for breaking the changeup commandment, either.


Mike Mussina: King of the Called Third Strike

Mike Mussina seems like the type of pitcher whose brilliance may get lost in the translation between traditional, back-of-the-baseball-card stats and sabermetrics. He falls thirty wins shy of the revered 300 club, and his career ERA (3.68) is way above that of the average Hall of Fame inductee (2.96). Some voters will take a cursory look at Mussina's candidacy and dismiss him as a good, but hardly dominant pitcher. Former Hall of Fame research associate and Cooperstown swami Bill Deane projects that Mussina will receive just seven percent of the vote -- precariously close to the five percent minimum required to stay on the ballot the following year.

But Mussina's bubble gum card stats ignore context -- the long-time Oriole and Yankee pitched in a high-scoring era, against lineups filled with sluggers in the cut-throat AL East division. Once you adjust for park factors and the go-go run-scoring environment of the 90s and early 2000s, Mussina easily clears the bar for enshrinement. His adjusted ERA is 23 percent above average, which ranks 13th all-time among starting pitchers logging at least 3,500 innings pitched. With 82.7 career Wins Above Replacement, Moose trumps the average Hall of Famer (69 WAR) and resides in the same neighborhood as Fergie Jenkins (82.7 WAR) and Bob Gibson (81.9 WAR).

Mussina managed to vanquish AL East hitters up until the end, recording one of his finest seasons in 2008 at age 39. He topped 200 innings and had a 131 ERA+, good for sixth among AL starters. Talk about finishing strong -- Mussina had the highest WAR total (5.2) among starters during his final major league season this side of Sandy Koufax (who had to retire at 30 due to a bum elbow) and Win Mercer (who committed suicide at age 28).

Highest WAR totals for SP in last MLB season


So, how did Mussina turn in arguably the finest season ever for a pitcher voluntarily calling it quits? He was the best in the game at freezing hitters in two-strike counts. Moose got the most strikeouts looking in the majors in 2008:

Called third strike leaders among starters, 2008

Mussina got the vast majority of those looking Ks with his fastball (36) and slider (20), and most of them (56 percent) came on pitches thrown just outside of the rule book-defined strike zone:

Location of Mussina's called third strikes, 2008

Hopefully, Hall of Fame voters study Mussina's pitching as thoroughly as these batters did. This guy deserves a plaque in Cooperstown.