Red Sox: Using SIERA and percentage metrics to analyze pitching staff

A look at the Red Sox pitching staff via advanced metrics

Major League Baseball Trade Rumors (MLBTR) is a resource site that I use frequently. MLBTR – especially Tim Dierkes – recently announced a change in their statistical approach to be used in articles. A transition will commence from K/9, BB/9, and K/BB to a new approach utilizing K%, BB%, and K-BB%. The outline is explained in detail here with further links to Fangraphs.

MLBTR also announced the use of SIERA (Skill-Interactive ERA), developed by MLBTR contributor Matt Swartz, as a preference over FIP and xFIP. Earned Run Average will continue to be used possibly as a statistical bone tossed to the more traditional-minded. And for those knuckle-dragging traditionalist (I plead guilty), W/L will appear about as often as the swallows to Capistrano.

"SIERA quantifies a pitcher’s performance by trying to eliminate factors the pitcher can’t control by himself. But unlike a stat such as xFIP, SIERA considers balls in play and adjusts for the type of ball in play.For example, if a pitcher has a high xFIP but has also induced a high proportion of grounders and pop-ups instead of line drives, his SIERA will be lower than his xFIP. – MLB Glossary"

Never one to let an opportunity to have the eyes of readers gloss over, I will look at SIERA first before plodding forward to the new percentages. Just how did our illustrious pitching staff perform in 2020? All are based on American League entries for comparisons.

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The Red Sox did have a “leader” or is it a loser (qualified) on the SIERA chart. Martin Perez managed a 5.43 which I quickly and brilliantly determined is not good. Perez also has been cut loose for obvious reasons. He also posted a 4.50 ERA. Being a quick read, I do notice a connection between an inflated ERA and an awful SIERA. I wish Perez well in his employment opportunities.

There are statistical quirks in SIERA just as there are in FIP in comparison to ERA. Dallas Keuchel had a forgettable 4.57 SIERA and a remarkable 1.99 ERA. Shane Bieber had a 1.63 ERA, so Keuchel was close. Bieber also had 2.52 SIERA – the best.

As a team, the Red Sox managed a 4.97 SIERA, just a notch below the Tigers at 5.00. Taking a further look at the Red Sox is a demonstration of abysmal pitching. If SIERA is a predictor of future performance opposing hitters will gleefully await the arrival of Boston. But all is not lost.

The positive news on the SIERA font is Nathan Eovaldi (3.45), Nick Pivetta (4.13), and rookie sensation Tanner Houck (4.15). There is an item of note and that is the much-maligned bullpen that actually performed reasonably well. A middle of the pack in the AL at 4.24. The Yankees – always a good comparison tool – checked in at 4.22. Closer in waiting Matt Barnes had a respectable 3.99.

The next MLBTR adventure is a statistical triumvirate of K%, BB%, and K-BB%. In 2020, the top-20 starting pitchers had a K% of at least 25, a BB% below about 7, and a K-BB% above about 18.

As a team, the Red Sox were eleventh in K% at 20.7%. Checked in with the worst BB% (10.2) in the AL and next to last (bless those Tigers!) with a 10.5 K-BB%. With ten or more innings Houck had a 33.3 K%, Pivetta 31%, and Eovaldi 26.1%. Barnes out of the bullpen had a 30.4%. Then comes the walks.

Sifting through the pitching detritus I will skip over the Kyle Hart’s of the staff and focus on just who may be around in 2021. Houck had a 14.3 BB%, Barnes 13.7%, Pivetta 11.9%, Ryan Weber 7.6%, and Eovaldi a minuscule 3.5%.

If a K-BB% in the 18 range is worthy then it bodes well for Eovaldi (20.6), Houck (19), and Pivetta (19). Ryan Brasier (17.3) and Barnes (16.7) are close. That is about it. Clearly, this is a staff that needs to keep giving away bases via walks that are too often converted to runs.

Since it starts with the rotation the positive is based on what MLBTR now uses there is Eovaldi, Pivetts, and Houck. All three performed well in the small sample of 2020.  In 2018, Chris Sale (2.27) had the best American League SIERA. And the best in 2017 (2.58). Eduardo Rodriguez posted a 4.31 SIERA in 2019.

Meanwhile, it is just a plethora of more numbers to digest and attempt to reasonable interpret. As a noted expression goes: “Facts are stubborn things, but statistics are pliable.”