Fantasy baseball: How to stream hitters

Christian Villanueva posted an OPS of 1.118 versus left-handers last season, but only .574 versus right-handers. Knowing when to start or sit a hitter can be the difference between winning and losing your league. Jake Roth/USA TODAY Sports

Beginning on the North American edition of Opening Day and lasting through the final day of the Major League Baseball regular season, I will once again be leading a team of writers bringing you ESPN's Daily Notes. The day preceding each slate, we pore through the matchups, identifying hitters and pitchers in favorable situations, all available in at least half of ESPN leagues. While each of the authors use slightly different criteria, there's a common core among the group. Here are some of the factors used in distinguishing hitters from one another on a daily basis.

Glossary of terms

The following terms are often incorporated into the hitter analysis in the Daily Notes.

Weighted on base average (wOBA): Features the components of on-base percentage but with coefficients for each term. The result is a gauge for how well a player generates runs. While not perfect, it's a decent proxy for overall fantasy potential, stolen bases excepted. Pitchers' wOBA against helps measure their effectiveness. Since 2011, the league average wOBA is .320, matching last season's mark. Note that wOBA is not park-corrected. The very best hitters can exceed .400. Anything over .350 is very good.

Weighted Runs Created Plus (wRC+): Expressed as an index with 100 being neutral, wRC+ is a normalized version of wOBA, accounting for park factors and era. Top batters post marks above 150. Hitters registering at least 120 are very productive.

Park Index: Also called park factor, it measures the extent the venue benefits or hinders specific events. The formula fleshes out team bias, comparing a team's performance at home and on the road. Since they're variable year-to-year, a three-year average is conventionally used. The most useful indices for evaluating batters are hits, homers, strikeouts, walks and runs. A factor of 100 is neutral. A venue aiding the metric by 10 percent is 110, while 90 suppresses by 10 percent. Rough guidelines:

Over 115: Extremely favorable. 106-115: Moderately favorable. 96-105: Neutral. 86-95: Moderately detrimental. Below 86: Extremely detrimental.

A positive index for hits, homers, walks and runs favors hitters. A negative factor for strikeouts benefits batters.

Strikeout rate: strikeouts/plate appearances. 2018 league average 22.3 percent. Excellent is below 15 percent. Troublesome is over 27 percent.

Walk rate: walks/plate appearances. 2018 league average: 8.5 percent

Contact rate: (at-bats - strikeouts)/at-bats. 2018 league average: 76.9 percent.

O-swing percentage: Commonly called chase rate, percentage of swings on pitches outside the zone. 2018 league average: 30.9 percent.

O-contact percentage: Percentage of contact on swings on pitches outside the zone. 2018 league average: 62.8 percent.

Z-swing percentage: Percentage of swings on pitches inside the zone. 2018 league average: 67.3 percent.

O-contact percent: Percentage of contact on swings on pitches inside the zone. 2018 league average: 85.5 percent.

Factors for evaluating hitters

Quality of opposing pitcher

In a landscape replete with burgeoning advanced metrics, sometimes Occam's razor is best. The primary litmus test is how good the guy throwing the baseball is. Ideally, pick on hurlers with a wOBA against above .325. It helps if the pitcher fans a low number of hitters -- anything below an 8.0 K/9 or 21 percent strikeout rate.

If you're looking specifically for a home run, some pitchers are more susceptible to the long ball. Target pitchers with a HR/9 over 1.3.

Included in every Daily Notes is a ranking of that day's probable starters, listed by Expected Game Score. The best targets check in at 45 or below. Anything less than 50 is a solid place to look.

Platoon splits

In general, you want a lefty swinger facing a righty thrower or vice versa. Here's the aggregate matchup data from last season, using wOBA:

  • LHB vs. RHP: 0.332

  • RHB vs. LHP 0.326

  • RHB vs. RHP 0.315

  • LHB vs. LHP 0.300

In-season platoon splits are not useful and can often be misleading. A right-handed batter doesn't own his split against southpaws until he faces them a collective 2,000 times, or about 10 seasons of full-time play. A left-handed batter requires 1,000 trips to the dish, or about five years of everyday action. So-called "reverse splits" are usually sample-size noise and not predictive.

Once a hitter has played a few years, it's viable to regress his career platoon split to league average. For example, if after five seasons a right-handed batter has recorded a .340 wOBA versus lefties, averaging .340 and .326 (league average) is a fair estimation of his expected platoon split. On the other hand, if a righty batter has a .326 wOBA versus southpaws after five seasons but carries a .340 in-season mark, it's inaccurate to contend he's figured out how to hit lefty pitching.

When selecting a left-handed hitter in the lineup against a righty starter, check to see if he's likely to be lifted for a pinch hitter if facing a lefty reliever. This might cost the batter an at-bat or two, reducing his opportunity to produce.

Batting order

Intuitively, the higher in the order, the better. Data from last season supports this.

The numbers for the first eight spots in the American and National Leagues are remarkably close, so they're lumped together. The rule of thumb is focusing on players in the first five spots.

If you're curious how the visiting team being assured of batting in the ninth affects the data, the guaranteed extra at-bat is balanced by the home-team advantage of scoring more runs at home. That is, there's no benefit using a hitter in a road affair hoping he gets an extra chance.

Park Index

While the venue is important, especially at the extremes, quality of opponent along with current weather conditions are far more relevant. Always choose a good hitter facing a poor pitcher in a pitchers' park over an average hitter facing an average pitcher in a hitters' park.

Wind blowing in can mitigate a home run park, while wind blowing out can aid a venue known to suppress power. The baseball carries more in warmer air. Keep in mind that average weather is baked into the park factor. That is, one of the reasons Globe Life Park is a hitters' venue is because it's usually hot in Arlington, Texas. Don't give extra credence to a batter on a warm night in Arlington -- it's already accounted for in the park factor.

Perhaps the key to using park factors is understanding that a favorable park for runs and one for homers are often mutually exclusive. There are many favorable home run venues playing neutral for runs, in large part due to fly balls not leaving the yard being caught more often in smaller outfields. On the other hand, there are some places where it's hard to clear the fences, but the real estate is so vast, many runs are scored without the benefit of a home run. What makes Coors Field so unique is Denver's thin air augments homers while the huge pasture makes for more hits, hence a double benefit to runs. The take-home message is if you're trolling for a homer, concentrate on the home run factor. If you're looking for overall run production, hone in on the run index. If you want a stolen base, play a speedster in a venue amplifying hits.

Batter versus pitcher

Usually abbreviated BvP, batter versus pitcher is a popular means of identifying strong matchups. Beware, the majority of research on the topic demonstrates BvP success isn't predictive. Please note, this is not the same as saying BvP doesn't exist. There very well might be certain hitters more likely to garner success facing certain pitchers. However, it's not possible to discern the actual instances from sample-size happenstance. That is, favoring a batter based on past success against his mound foe does not increase probability of continued success. In other words, judge a hitter's substantial body of work versus all left-handers (see earlier) rather than his small body of work against this particular left-hander.

Hot and cold streaks

Much like BvP, streaks might be real, but being on a hot streak does not elevate chances of another solid performance, just as cold streaks can be snapped at any time. That said, if a cold streak is accompanied by the hitter chasing more pitches out of the zone (O-swing percentage), I'm reluctant to trust the batter, especially against a pitcher with an above-average strikeout clip.

Stolen bases

In rotisserie leagues, a great way to fortify stolen base totals is identifying individual matchups favoring the hitter. Included in the Daily Notes is a hitting chart pulled from Tristan Cockcroft's Forecaster. This is a great starting point. However, it uses caught stealing numbers for the team, not necessarily the backstop squatting that day. Once lineups are announced, usually at least an hour before first pitch, the ability of the active catcher can be gleaned. Last season, the league success rate was 72 percent. Picking on receivers with rate below 25 percent is recipe for success while avoiding those above 32 percent is prudent, unless the hitter exhibits proficiency in the 80 percent range.

An overlooked element of base stealing is spot in the batting order. The individual player's tendency is far more important, but it helps to have an idea how lineup position might influence green light/red light.

Aside from the observation there were more pilfers in the American League than National League last season, and that it projects in that manner again for 2019, of particular note is that it's defensible to deploy a batter occupying a bottom-of-the-order spot in the junior circuit, despite the likelihood they're short one at-bat compared to the rest of the team.

General thoughts

Especially when planning for Monday and Thursday lineups, it's best to be ahead of the curve and acquire free agents the day (or night) before intending to use them. Wait until the game begins for the player you want to drop, then make the pickup. You get the pick of the litter before others thin the herd.

Bullpens are becoming an increasingly important aspect of today's game. A lot depends on game flow, since the better relievers will work in close games, but the overall quality of the bullpen can influence decisions. Using a hitter against a lesser pitcher on a club with a strong relief corps is a risk. If the pitcher escapes for a few innings, he passes the baton to better pitchers. You'd best hope for early production given the chance of an overall non-productive effort. That said, if the offense gets to the lesser pitcher, the ensuing parade could feature weak arms, forced to take one for the team.

Because it's so important, let's reiterate the first point. Everything discussed here can be useful in the decision-making process. However, sometimes it's best not to overthink. There's nothing better than a better hitter facing a lesser pitcher.