The Z Files: Streaming Pitchers for Fun and Profit

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Updated on September 6, 2018 12:23PM EST

One of the most important tasks a fantasy GM faces over the next three-plus weeks will be identifying favorable matchups in which to stream pitchers. Quality of opposing lineup, in terms of both production and strikeout potential, is paramount to the evaluation.

Here's the problem. There isn't a reliable sample size to use as a basis. How long should we be looking back to get the truest read on the current level of expected performance? A week? Month? Season to date?

Sorry, but I don't have the answer, at least not yet. To be honest, I'm not sure there is an answer, though there likely is, with the caveat outliers are likely. What I do have is a bunch of data, looking back at the entire season, since the All-Star break, the last 30 days and the last week.

Even though it's flawed, weighted on base average (wOBA) will be used to gauge strength of opposing lineup as well as strikeout percentage (K%). Each metric will be parsed by team versus right-handed and left-handed pitching.

Let's begin with numbers versus right-handers:

Team	season wOBA	2H wOBA	30 day wOBA	7 day wOBA	season K%	2H K%	30 day K%	7 day K%
Average	0.323	0.328	0.325	0.326	22.1%	21.9%	22.0%	22.6%
Arizona Diamondbacks	0.309	0.330	0.307	0.262	23.8%	22.4%	23.1%	24.5%
Atlanta Braves	0.320	0.327	0.314	0.309	20.5%	20.2%	20.3%	23.7%
Baltimore Orioles	0.314	0.350	0.332	0.313	23.7%	22.2%	22.3%	20.2%
Boston Red Sox	0.354	0.345	0.349	0.344	18.8%	19.4%

Let's begin with numbers versus right-handers:

Team	season wOBA	2H wOBA	30 day wOBA	7 day wOBA	season K%	2H K%	30 day K%	7 day K%
Average	0.323	0.328	0.325	0.326	22.1%	21.9%	22.0%	22.6%
Arizona Diamondbacks	0.309	0.330	0.307	0.262	23.8%	22.4%	23.1%	24.5%
Atlanta Braves	0.320	0.327	0.314	0.309	20.5%	20.2%	20.3%	23.7%
Baltimore Orioles	0.314	0.350	0.332	0.313	23.7%	22.2%	22.3%	20.2%
Boston Red Sox	0.354	0.345	0.349	0.344	18.8%	19.4%	19.6%	19.3%
Chicago Cubs	0.335	0.322	0.317	0.316	21.3%	21.9%	24.2%	28.8%
Cincinnati Reds	0.323	0.310	0.310	0.367	21.5%	22.9%	22.5%	21.3%
Cleveland Indians	0.339	0.346	0.344	0.315	19.0%	14.9%	16.3%	19.9%
Colorado Rockies	0.318	0.307	0.310	0.277	23.4%	24.0%	22.6%	19.4%
Chicago White Sox	0.317	0.326	0.314	0.321	25.5%	25.7%	26.4%	26.8%
Detroit Tigers	0.297	0.301	0.318	0.341	22.6%	23.4%	23.3%	31.8%
Houston Astros	0.325	0.299	0.302	0.300	19.8%	20.0%	20.4%	16.3%
Kansas City Royals	0.314	0.354	0.367	0.418	20.5%	21.8%	22.4%	21.8%
Los Angeles Angels	0.332	0.339	0.301	0.235	21.1%	23.9%	24.6%	32.5%
Los Angeles Dodgers	0.344	0.353	0.340	0.362	22.4%	24.2%	23.7%	19.8%
Miami Marlins	0.300	0.281	0.286	0.347	22.4%	22.2%	20.0%	19.2%
Milwaukee Brewers	0.330	0.344	0.353	0.408	24.7%	23.2%	23.2%	19.4%
Minnesota Twins	0.323	0.327	0.327	0.326	21.8%	23.2%	23.7%	25.5%
New York Mets	0.318	0.332	0.343	0.344	21.6%	21.7%	21.2%	17.6%
New York Yankees	0.340	0.338	0.350	0.331	22.6%	20.5%	21.1%	23.8%
Oakland Athletics	0.336	0.343	0.340	0.342	21.8%	21.1%	22.2%	25.6%
Philadelphia Phillies	0.320	0.323	0.318	0.332	25.0%	23.4%	21.2%	21.7%
Pittsburgh Pirates	0.317	0.316	0.279	0.258	19.7%	20.2%	21.2%	19.1%
San Diego Padres	0.293	0.296	0.306	0.283	25.8%	25.7%	26.3%	25.4%
Seattle Mariners	0.322	0.320	0.329	0.300	20.0%	19.2%	19.3%	15.1%
San Francisco Giants	0.302	0.267	0.260	0.258	24.1%	25.5%	25.5%	28.8%
St. Louis Cardinals	0.321	0.326	0.338	0.327	22.2%	21.7%	22.7%	26.7%
Tampa Bay Rays	0.324	0.332	0.345	0.382	22.2%	21.3%	21.5%	21.9%
Texas Rangers	0.330	0.368	0.365	0.387	24.6%	22.8%	20.0%	21.7%
Toronto Blue Jays	0.332	0.345	0.341	0.318	22.5%	20.7%	21.1%	18.3%
Washington Nationals	0.331	0.352	0.346	0.335	20.1%	18.5%	18.4%	22.7%

I'm planning a more comprehensive study in the offseason, so for now I'll just make some observations. I'm pleasantly surprised how many teams are consistent with respect to year-to-date versus more recent samples. That said, there's some notable exceptions.

The Orioles have been more productive over the second half, but if you made that adjustment the past week, you'd be disappointed since they haven't hit as well lately.

The Tigers are below average for the season, though they've improved the last month. Even so, they were still below average until the past week.

The Astros are an average offense for the year, but haven't been especially daunting over the second half, even as they've gotten some of their best hitters back from injury the last few weeks.

The Royals are below average for the season but have been crushing righties lately, especially the last week.

The Mets are overall below average but have been productive since the break.

The Pirates have been below average with a righty on the hill all season, but lately they've been among the worst clubs in the game.

The Giants are like the Bucs, but even more extreme.

The Rays are an average lineup in total but have been hitting righties much better as the season progresses.

Now let's check out the data versus southpaws:

Team	season wOBA	2H wOBA	30 day wOBA	7 day wOBA	season K%	2H K%	30 day K%	7 day K%
Average	0.319	0.316	0.314	0.298	22.2%	21.9%	22.3%	23.1%
Arizona Diamondbacks	0.328	0.319	0.325	0.256	22.9%	21.9%	22.8%	20.8%
Atlanta Braves	0.346	0.332	0.359	0.327	19.7%	19.1%	17.7%	17.1%
Baltimore Orioles	0.293	0.289	0.260	0.387	21.8%	23.7%	24.7%	14.1%
Boston Red Sox	0.325	0.320	0.324	0.362	22.6%	21.0%	19.6%	14.6%
Chicago Cubs	0.329	0.324	0.315	0.225	22.2%	23.2%	24.5%	26.5%
Cincinnati Reds	0.340	0.342	0.357	0.317	20.5%	20.0%	19.3%	14.1%
Cleveland Indians	0.329	0.308	0.265	0.269	19.1%	19.5%	21.9%	22.4%
Colorado Rockies	0.349	0.354	0.340	0.317	21.5%	20.2%	21.8%	22.9%
Chicago White Sox	0.314	0.324	0.350	0.338	27.0%	29.5%	30.4%	31.9%
Detroit Tigers	0.319	0.283	0.295	0.333	20.5%	21.4%	21.5%	20.5%
Houston Astros	0.357	0.372	0.411	0.252	19.6%	17.8%	17.3%	27.3%
Kansas City Royals	0.292	0.278	0.254	0.351	23.6%	24.7%	23.6%	18.2%
Los Angeles Angels	0.294	0.283	0.302	0.267	21.1%	22.4%	20.3%	25.8%
Los Angeles Dodgers	0.313	0.310	0.336	0.292	22.8%	24.2%	24.0%	34.2%
Miami Marlins	0.296	0.307	0.322	0.343	21.8%	21.6%	26.9%	19.6%
Milwaukee Brewers	0.321	0.346	0.372	0.290	20.4%	19.7%	18.1%	19.8%
Minnesota Twins	0.302	0.285	0.308	0.278	23.2%	21.9%	20.5%	21.1%
New York Mets	0.290	0.304	0.312	0.280	24.8%	22.1%	21.4%	25.0%
New York Yankees	0.348	0.309	0.284	0.307	23.0%	22.1%	21.7%	27.3%
Oakland Athletics	0.330	0.366	0.350	0.288	22.5%	20.1%	21.3%	23.6%
Philadelphia Phillies	0.302	0.298	0.282	0.231	23.5%	24.4%	26.8%	29.3%
Pittsburgh Pirates	0.321	0.316	0.324	0.308	21.7%	22.5%	20.6%	18.8%
San Diego Padres	0.310	0.316	0.329	0.320	24.3%	23.7%	23.6%	20.0%
Seattle Mariners	0.312	0.279	0.278	0.301	20.2%	17.7%	19.8%	21.9%
San Francisco Giants	0.301	0.287	0.264	0.274	22.2%	24.4%	28.2%	35.9%
St. Louis Cardinals	0.336	0.382	0.352	0.308	21.3%	16.7%	18.2%	32.1%
Tampa Bay Rays	0.323	0.317	0.289	0.289	23.5%	22.3%	23.4%	27.1%
Texas Rangers	0.322	0.312	0.284	0.294	22.9%	21.9%	22.3%	19.2%
Toronto Blue Jays	0.311	0.307	0.293	0.275	21.7%	22.1%	21.7%	18.5%
Washington Nationals	0.318	0.315	0.293	0.404	23.1%	24.6%	25.5%	17.4%

The Diamondbacks have been average all season but if you didn't use your lefty against them the past week, you're not happy.

The Orioles have been terrible facing lefties for the season, except the last seven days where they've crushed it.

The Cubs are the opposite of the Orioles, as they've been terrible versus southpaws lately.

The Indians have been a little above average most of the season but have struggled versus lefties for the past month, so there's a good chance many have missed chances to stream southpaws versus the Tribe.

The Astros have crushed lefties all season, save for the past week.

The Royals are the antithesis of the Astros, sluggish all season against LHP before slugging against them the past week.

The Marlins are below average for the season but have really picked up the pace when a lefty toes the rubber over the second half.

The Brewers have raked versus lefties, but not the last week.

The Phillies have been below average most of the season but have gotten progressively worse.

The Nationals had been trending downward before exploding the past week.

GENERAL OBSERVATIONS

The above is not meant to be comprehensive or even that analytical. It's mainly designed to show even when the range is fine-tuned, there will be exceptions, frustrating those of us streaming starters for perceived favorable matchups, or perhaps avoiding seemingly tough ones.

The smaller the sample, the more the specific hurlers come into play. If a team draws the Dodgers and Clayton Kershaw, Alex Wood and Rich Hill, their recent performance against lefties is likely to be subpar. On the other hand, if a club squares off with a weak staff, maybe the Rangers or Orioles in their hitter-friendly venues, their production against right-handers is apt to be embellished.

The final point I'd like to address is variance. I am literally shocked that the variance between lefty and righty splits isn't more exaggerated. I expected the lefty numbers to be all over the place, but via some standard deviation analysis, left-handed data is just a little more variant. This bodes well for the eventual study, providing some encouragement to carry it through. That said, as demonstrated, there will always be short-sample outliers.

To anticipate the question, for my own teams I use numbers from the past month to ballpark the quality of opposition, taking into consideration quality of opponent over that time as well as venue and extraneous factors like weather. I'll also think about recent lineups. Did someone get hurt or come back from injury? Did they make a trade or call up a prospect? In other words, like most things, I employ a combination of subjective and objective measures, trying to find the balance between recency bias and season-long numbers which may no longer reflect current performance.