Investigating Felix Hernandez's Modified Arsenal

While much of the focus on the Seattle Mariners this offseason will remain on how vastly improved the club's offense will be with Robinson Cano now in the fold -- and rightfully so given Seattle's offensive ineptitude last season -- one aspect that cannot be overlooked is staff ace Felix Hernandez's tremendous arsenal changes last season.

With respect to value, 2013 was not Hernandez's best campaign as a professional. Over 31 starts, the now 27-year-old posted a 3.04 ERA and 1.13 WHIP (slightly better than his 3.20 ERA and 1.20 WHIP career marks) en route to a 5.2 bWAR, which was good enough to be his third-highest season wins mark. Yet while these numbers weren't quite on par with his Cy Young award-winning 2010 season in which he posted a league-best 2.27 ERA and 1.05 WHIP, Hernandez was noticeably better last season with respect to strikeouts -- hoarding a career-best 9.5 punchouts per nine innings.

As it turns out, Hernandez's increased strikeout rate stemmed from an abrupt adjustment in pitch usage.

Comparing Hernandez's Pitch Usage and Strikeout Rate, 2008-2013

The graph above depicts Hernandez's pitch usage since his age 22 season in 2008, dividing his arsenal into two categories: 'Hard' stuff (i.e. fastball, sinker, cutter, splitter) and 'soft' stuff (changeup, curveball, slider). With that, I've included Hernandez's strikeout rate, which is shown by the gray line at the bottom. A few things we see right off the bat include:

• Hernandez's reliance on fastball variations (or 'hard' stuff, in this case) decreased progressively from 2008 to 2012, declining 5.8% on average each season to the point where he threw less fastballs in 2012 (46.7%) than non-fastballs (53.3%). That changed last season, as Hernandez reverted back to a reliance on his hard stuff, throwing fastball variations 66.8% of the time.
• Consequently, only one third (33.2%) of Hernandez's offerings last season were 'soft' offerings -- nearly 20 percent lower than that of his 2012 campaign in which a career-high 53.2 percent of his offerings were non-fastballs.
• Hernandez's strikeout rate has been on a steady incline, increasing from 20.4% in 2008 to a career-best 26.3% in 2013 (enough for a 0.98% average boost per season).

The question now becomes: Exactly what caused the abrupt increase in 'hard' stuff last season? Another look at pitch usage reveals everything.

Comparing Hernandez's 'Hard' Offerings Usage

This next graph shows Hernandez's use of his three 'hard' offerings (fastball, sinker, cutter) over the past two seasons. In 2012, King Felix utilized his fastball most often, throwing it at a 48.8% clip while mixing in his sinker and cutter at essentially the same rate (26.6% and 25.3%, respectively). Last season was a far cry from 2012, as Hernandez's sinker became his most frequent fastball variation by tossing it 51.8% of the time -- nearly twice as often as the previous season. His four-seam fastball rate declined slightly to 42%, and he went to his cutter at a 6.2% rate -- nearly 20% lower than in 2012.

Taking a look at how Hernandez's command of his sinker improved over the past two seasons, it's no wonder he went to it so frequently.

Hernandez sinker pitch frequency, 2012 vs. 2013

Hernandez's sinker command adjustments weren't obvious, but they were enough to make a significant difference. In 2012, Hernandez located his sinker in the 'down' portion of the zone at a 40.4% rate, and opponents posted a .396 batting average against the offering -- the highest mark against any qualifying starter's sinker that year -- to go with a strikeout rate of 7.4%, which was second worst among qualified starters. Last season, he placed the pitch 'down' 53.3% of the time and batters struggled against it, generating a .264 batting average while striking out at a 23.1% clip, which was second best among qualified rotation arms.

What we've learned is that when Hernandez locates his sinker 'down', as he did in 2013, the pitch is a lethal offering with a high strikeout capacity. Due to the offering's success, he reduced his reliance on 'soft' pitches yet increased his strikeout rate.