How often should Marcus Stroman throw his sinker?

In case you missed it, on Friday a fascinating piece of research by Matthew Murphy was published at the Hardball Times.

Titled Are Groundball Pitchers Overrated?, Murphy examines why groundball-heavy pitchers as a group underperform not only their peripherals but also allow more runs than low groundball rate and average groundball rate pitchers. As he states in his introduction:

So, if ground balls are good for pitchers, and inducing them is a repeatable skill, then why aren’t pitchers who induce ground balls getting better results?

This post is mostly an excuse to an absolutely fantastic article, which you all should read if you haven’t already before we go any further, but I also wanted to look at how this research could potentially impact the Toronto Blue Jays electric young starting pitcher, Marcus Stroman.

Stroman, as has been written about here and other outlets, significantly increased his use of a two-seam or sinking fastball after discovering the pitch just this summer. By the end of the season, he was throwing it more than twice as often as any other individual pitch.

His groundball percentage, as one would expect, also increased each month mostly thanks to his increased sinker usage:

June 2014 – 43% GB, 68 ERA-, 92 FIP-, 3.69 xFIP, 3.63 SIERA (497 pitches)

July 2014 – 51.8% GB, 43 ERA-, 60 FIP-, 2.99 xFIP, 3.01 SIERA (509 pitches)

August 2014 – 58.1% GB, 171 ERA-, 84 FIP-, 3.61 xFIP, 3.64 SIERA (427 pitches)

September 2014 – 58.9% GB, 66 ERA-, 56 FIP-, 2.54 xFIP, 2.46 SIERA (426 pitches)

Courtesy FanGraphs

It becomes clear looking at his numbers over the last month of the season why Stroman kept relying on his sinker so heavily – it was working. His xFIP and SIERA were both sparkling but he also walked only 2.5% of batters over this stretch while he hovered between 6% and 7% each other month of the season. There’s a chance he simply became more comfortable with his primary pitch and started to locate it better but it’s probably more reasonable to assume he’ll regress somewhat to the norm.

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What I’m attempting to figure, albeit likely in vain, is whether or not Stroman should continue to throw more than 40% sinking fastballs with the aim of keeping the ball on the ground more than 50% of the time. Based on Murphy’s research, ground ball pitchers in general don’t perform as well as pitchers with a more balanced approach. He identifies Clayton Kershaw, Madison Bumgarner, David Price and Cole Hamels as four elite pitchers with GB rates nearly identical to their FB rates. Pitchers in the group with “average” BIP profiles outperformed those with more extreme FB or GB rates in ERA, FIP and xFIP.

When taking this sample to the individual level, we can look at specific variables that may or may not impact Marcus Stroman’s success with his sinker compared to the average pitcher.

1. He makes approximately half his starts within the confines of the Rogers Centre, which has been a launching pad for home runs the past several seasons. It makes sense to want to keep the ball down more often in this environment than say Petco Park in San Diego. The turf is also supposed to play slower this season, which in theory should give infielders more time to get to groundballs.

2. He’s short. As much as possible I try not to bring up Stroman’s size when analyzing him. However, the fact he’s only 5’8 means pitches up in the zone come at a flatter plane towards the hitter, which makes lifting the ball with power easier since it’s not “bearing down”. Stroman’s sinker gives him some natural plane when working down in the zone.

3. His projected middle infielders are Jose Reyes and Maicer Izturis. The pair has combined for -51 defensive runs saved over the past three seasons. That’s not good. Josh Donaldson at the hot corner should help but it’s still enough to give a pitcher pause if he hopes to execute a groundball-heavy gameplan.

4. Keeping the ball in play can allow him to pitch longer into games. Strikeouts are great, but they come at a cost and that’s pitch count. Stroman acknowledged during his interview with Charlie Caskey of Your Van C’s that he was a high strikeout pitcher in the minors but was never able to pitch late into games. Switching up his focus to soft contact helped him toss his first ever Maddux in September with a complete game shutout on only 93 pitches against the Chicago Cubs.

So what should Stroman do? Should he continue throwing an obscene amount of sinkers based on the above factors? Or should he tone down his sinker usage as opponents adjust to his weapon of choice?

The truth is, I don’t really know the answer. My gut tells me he would be best served by flashing his absurd set of pitch comps to keep hitters off-balance. However there’s also a chance he could excel as a groundball specialist. Either way I’m excited to see how Marcus Stroman chooses to approach the 2015 season and whether or not he’s able to maintain or improve on his success from last year.