Statcast Pitcher Risers/Fallers - Two-Strike xBA (Week 6)

Welcome back to Rotoballer's series using Statcast to extrapolate, dig into, and commiserate over data to examine pitching performances. The weekly series will be dynamic as we fine-tune our findings and I enlighten myself on the information and tools at my disposal.

For Week 6, we'll continue our theme from last week arguing that by May, starting pitchers have had enough opportunities to approach a steady-state in performance volatility. Of course, fortunes, health and countless external variables affect every pitcher's one-off outings throughout the season, but we fantasy owners no longer need to freak out about a bad start from Justin Verlander or debate whether Lucas Giolito is worth rostering.

We'll drill deeper this week and look at expected batting average (xBA) for pitchers with two-strike counts. xBA is a metric combining strikeouts with Statcast data to determine the fielding-independent hit probability of a batted-ball event (BBE). We'll compare xBA with actual batting average (BA) to determine which pitchers might be unlucky setting down batters and which are oddly skating out of trouble too often. With any two-strike count, a pitcher has a meaningful advantage (.159 median BA) over a hitter compared to any count with zero or one strike (.323). Our thesis today is pitchers with a lower xBA than BA on two-strike counts should improve their ability to close-out at-bats moving forward and those with a higher xBA should see their BBEs eventually turn against them.

Bound to Pop

All stats as of May 7, 2018 for 116 qualified pitchers that have thrown over 500 pitches

James Paxton, Seattle Mariners - 1-1, 4.19 ERA, 1.32 WHIP, 13.97 K/9

James Paxton was off to a meddling start before his 16-strikeout explosion May 2 against the Athletics (7 IP, 0 ER, 5 H, 1 BB). The outing launched him to the top of the leaderboard in K/9 but his other numbers haven't been impressive. Paxton ranks 93rd in two-strike BA (.202) but 39th in xBA (.154). The delta of .048 is fourth widest in the majors.

The most encouraging sign is Paxton's FIP which sits at a tidy 3.05. Even before fanning 16 last week, Paxton boasted a healthy 12.51 K/9. His velocity seems fine, and the SwStr% (14.6%) and Contact% (71.3%) are better than 2017. However, when batters aren't whiffing, they're hitting him hard (34.1% Hard%) to a tune of a .349 BABIP. His FB% has inexplicably jumped to 47.2% from 32.7%, negatively compounding a 11.9% HR/FB which is his highest mark since 2013.

If we believe in mean reversion, and studies have shown BABIP and exit velocity (EV) have some year-on-year relationship, then Paxton's BABIP should dip about 40 points and his current FB/LD 91.7 MPH EV will decelerate modestly. The prevailing extreme fly ball tendency is well off his career rate of 31.2% so that should gradually alleviate the HR/FB pressures. Paxton will have an opportunity to follow-up his stellar performance this week against the Toronto Blue Jays.

Eduardo Rodriguez, Boston Red Sox - 3-0, 5.29 ERA, 1.27 WHIP, 10.86 K/9

Eduardo Rodriguez ranks higher than Paxton (23rd) in two-strike xBA at .142 but his .189 BA (85th) gives him the major's fifth widest mark (.047). For the season, Rodriguez has mixed in three quality starts with three clunkers. He holds a solid 3.00 K/BB but has been the victim of a 15.8% HR/FB. Not a complementary figure for a fly ball-heavy pitcher (44.7%).

Positively, Rodriguez' Hard% of 30.6% isn't alarming and is in-line with his profile last season. For 126 pitchers with at least 80 BBEs this season, his 90.5 MPH FB/LD EV is 13th lowest. He's been able to achieve swings and misses (13.3% SwStr%) but his issue with retiring batters could be a Zone% that is just 39.3%. Two luck-related factors that won't help his cause is an abnormally low LD% (10.6%) and .278 BABIP that would probably rise before falling.

With his 4.55 FIP, Rodriguez won't fool anyone into believing he's an ace. Although still only 25, his career has been marred with inconsistency and injuries. However, he could still be a useful fantasy asset, especially in wins for a high-octane Red Sox team. If Rodriguez improves on pounding the strike zone, he may not let batters get away, normalizing his headline numbers to a more tolerable level. He'll visit the Yankees in the Bronx later this weekend.

Other possible underachievers: Luke Weaver (STL, .044 BA-xBA), Nick Pivetta (PHI, .040), Julio Teheran (ATL, .039)

Due to Drop

Trevor Williams, Pittsburg Pirates - 4-2, 2.63 ERA, 1.10 WHIP, 5.71 K/9

The Trevor Williams fantasy bandwagon suffered its first speedbump on May 3 when he couldn't make it out of the sixth inning and suffered his second loss (5.2 IP, 3 ER, 4 H, 1 BB, 3 K). But outside of strikeouts, Williams has been great with five quality starts in seven outings. He's getting batters to swing outside the zone and inducing weak contact (23.7% Soft%).

However, Williams' -.063 delta between his two-strike BA (.116) and xBA (.179) grades as third luckiest. A 4.15 FIP suggests his performance could be more mirage than magic. Despite the strong WHIP, Williams is issuing free passes at the highest rate of his career (3.95 BB/9). Couple that with the subpar strikeouts and his 1.44 K/BB ranks 88th out of 93 qualified pitchers. The fortuitous BA and WHIP are buoyed by a .209 BABIP that is seventh lowest in the majors.

The erosion in his strikeout profile from a 7.0 K/9 last year could be due to falling velocity across the board. At his current 40.4% FB% pace, a tick up in HR/FB from 6.5% to his average 10.5% could swiftly impair his fantasy value. Unless Williams can boost the strikeouts, the ongoing revelation doesn't appear sustainable. He will visit the Chicago White Sox this week.

Gio Gonzalez, Washington Nationals - 4-2, 2.33 ERA, 1.34 WHIP, 9.78 K/9

Gio Gonzalez has been a reliable pitcher since his debut in 2008 and off to hot start in 2018. Regarding two-strike BA (.116) and xBA (.170), his -.054 differential is fifth luckiest. He and Williams are tied for 13th-lowest two-strike BA this season. The positives for Gonzalez is his FIP (2.56) meshes with the ERA and a .321 BABIP indicates external fortunes might be working against him.

Gonzalez' WHIP tells a different story. He's had problems with command (3.72 BB/9), preventing him from going past six innings in five of seven starts. Despite a FB/LD exit velocity that's risen a full 3 MPH to 94.5 this season, his HR/FB sits at a microscopic 2.9%. The strikeout figures have been impressive, but his structural declining fastball velocity puts more pressure on executing on a changeup that's been his bread-and-butter pitch.

Gonzalez should certainly be a serviceable pitcher for fantasy owners. The strikeouts and supporting cast should maintain his value season-long. But according to xBA, Gonzalez is just about average with two strikes on hitters. His messy WHIP and lack of endurance to pitch deep into games jives with the Statcast expected results. It shouldn't be surprising if Gonzalez sees his ERA creep closer to 3.00, which would still hold water anywhere. His next test comes against the Padres in San Diego.

Other possible overachievers: Jose Quintana (CHC, -.075 BA-xBA), Jake Junis (KC, -.052), Cole Hamels (TEX, -.042).

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