RADIO
Pierre Camus evaluates the importance of rolling window statistical analysis for hitters to identify risers and fallers in fantasy baseball throughout the season.
"It's a marathon, not a sprint." This axiom is one of the most tired expressions in all of baseball and is often used to prevent us from ascribing significance to a slump. The baseball season is the longest among all professional sports, spanning 162 games and six months, not including spring training and postseason action.
"Death, taxes, and statistical regression to the mean..." is a less popular phrase that is known among some in the sabermetric community. Simply put, what goes up must come down and vice versa. Yet, the fantasy community tends to constantly overreact to streaks and slumps alike, vastly overvaluing hot players and giving up too soon on certain players as well.
We've previously examined the validity of juxtaposing a 60-game data sample over a full season to that of an abbreviated 2020 season. The short season didn't allow time for things to change much in-season but we're back to a full schedule, which means readjusting our thinking to reflect the marathon mindset. Although it is a long, winding season, it really isn't a marathon so much as a series of sprints, at least statistically speaking.
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Streaming Services
We all know the concept of streaming. At RotoBaller, we offer daily streamer options for hitters and pitchers based on matchups. This does take recent performance into account as well, but it's not just a matter of who's hot. A strong streamer is based on hitter vs pitcher matchup, LvR splits, ballpark factors, weather, and, of course, availability.
Some of us don't have the luxury to pick through the waiver wire every single day or play in leagues with weekly transactions. That makes it a little trickier because you have to take into account the number of games played in a given week and what the schedule looks like for those seven days. That affords you the chance to take into account home/road splits and strength of opponent but pitching matchups aren't always set in stone that far ahead. That makes it more important to look into how a hitter is performing overall to determine if he can sustain fantasy production over a week or two regardless of opponent.
Too often, we look at season-long stats when evaluating players, especially toward the second half. But there's a reason all fantasy platforms have a filter for the last 7/14/30 days. Most hitters perform unpredictably on a daily basis, much less a weekly basis.
A very smart analyst by the name of Jon Anderson, who happens to write for RotoBaller now, examined the notion of whether hot and cold streaks are real. His findings: of course streaks themselves are real but they don't hold enough of a correlation to future production to buy into.
For DFS players, the advice is clear: "buy into hitters when their salaries are depressed because of poor recent performance."
What about season-long fantasy leagues? You can't just add and drop players willy nilly. In most competitive leagues, the most consistent hitters are already rostered so you're left with rookies, journeyman, and unproven commodities on waivers. Some of these players turn into keepers but most fade just as quickly as they flash. This is where we use another tool at our disposal thanks to Statcast - rolling windows.
The Value of Rolling Windows
Rolling windows show a player's performance in a selected stat over the most recent number of plate appearances selected. Currently, we are able to examine BA, xBA, SLG, xSLG, wOBA, and xwOBA. Each stat has value for a different reason and can tell a different story, depending on the number of PA selected.
There are 111 players currently over the 250 PA threshold, which means all others would extend back to 2020 if using that sample size. A sample of 50 PA is two weeks, more or less, which can give a good glimpse into a player's short-term effectiveness.
Finding players like Juan Soto and Pete Alonso at the bottom of the xSLG leaderboard or Nolan Arenado at the bottom of the xBA list over the past 50 plate appearances is jarring but accurate. Ideally, you would have benched these players over the last couple of weeks but at the same time that would have been a terrible idea.
Soto's xSLG is down by .351 in a 50-PA window but it's up by .124 over a 100-PA window. He's the type of player that doesn't stay down for long and can't effectively be replaced by anyone on your bench. Predicting slumps, especially among stud players, is almost impossible. Predicting regression isn't quite as hard, it's just a matter of timing.
2021 Case Studies
Adalberto Mondesi, Kansas City Royals
Mondesi is the embodiment of a sabermetric roller coaster. Never one to be found stuck in the middle, he is either blazing hot or ice cold. Turns out, he's still on fire after last year's ridiculous finish, now that he's finally suited up this season.
You're loving life if you have Mondesi on your roster at the moment but the concern is that once he slows down, he'll crash like the market on Black Monday. We've seen how low he can go and don't want to be left holding on to a hitter in the midst of an 0-for-35 streak when we could have sold high.
Of course, you can't sell now because it's not really about batting average with him. The steals will carry his fantasy value - the BA is just gravy really.
Kyle Schwarber, Washington Nationals
It didn't take another two-homer night against the Marlins to put Schwarbs at the top of the slugging leaderboard but it didn't hurt either. He has a .956 xSLG over his past 50 PA on the strength of eight homers in the past five games. After hitting two homers in all of April, he's gone yard 12 times in the past 12 days.
How has he caught fire all of a sudden? He admitted he doesn't even know although his swing is in a good place. Still, he acknowledged it won't last.
“It’s the reality of this game that you know what, I’m probably not going to keep doing this the whole year. It’s physically impossible to keep doing this..."
In other words, sell now if at all possible. Not just in an attempt to take advantage of his sky-high stock but to avoid having him in your lineup when the O-fers start coming. Schwarber has incredible power, ranking among the leaders in barrel rate four of the last seasons, but he also has a career .232 batting average and 28.2% strikeout rate.
Also worth noting, 20 of his home runs this season have come against right-handers; he's batting .215 with a total of one homer and five RBI against left-handers. If you're lucky enough to have Schwarber on your roster, he should be sitting against lefties. Then trade him ASAP.
Austin Riley, Atlanta Braves
A glance at Riley's seasonal stats shows improvement across the board, including an expected slash line of .258/.349/.473. His .276 average is downright delightful for someone who hit .239 and .226 the past two seasons. But this doesn't tell the true tale of his 2021 season.
For the first three weeks of the season, he was unplayable in fantasy leagues. He was batting .182 with zero homers and one RBI through the first 15 games and didn't hit his first home run until April 21.
From that point on, he became one of the hottest batters in the league, slashing .355/.442/.700 with 10 HR, 21 RBI, 22 R over the next 129 plate appearances. His season average was up to .313 and it looked like he was on the verge of a breakout season. Guess what happened next?
Riley is batting .209 with only two homers in the 95 PA since that point in time, back to being benchworthy.
Riley's rolling windows may simply reflect a streaky hitter. His rookie season was marked by a torrid debut in which he hit .324 with nine HR with 25 RBI in his first 18 games before falling off dramatically with a nearly 100-point drop in batting average the rest of the way.
There may be more to his latest slump, however, as is closely coincides with the absence of Marcell Ozuna since May 26. Riley struggled in the cleanup spot and may have benefited more than we realize from the lineup support of last year's MVP runner-up. Expect another uptick but not as dramatic as the one he enjoyed in May.
Freddie Freeman, Atlanta Braves
It would be hard to expect Freeman to repeat last year's output but he's put up solid numbers, especially in the power department. Yet, Freeman's 250-PA rolling window for xwOBA highlights the fact that nobody is immune to the powerful force of regression.
The fact he's at the bottom of this list is a testament to how outstanding he was in 2020. Notice that his .392 xwOBA is far higher than those other names and his .410 xwOBA on the season ranks 11th among qualified hitters. Rolling windows, like any stat, can be misleading if read incorrectly. Freeman is still one of the best hitters in the majors, just not as dominant as he was at the end of last season.
Yermin Mercedes, Chicago White Sox
Not to end on a sour note but Mercedes is the perfect example of the importance of evaluating players based on present production, not past. What has he done for us lately? Not much.
As soon as the calendar turned to May, his average fell below .400 and keep plunging. If you've kept Mercedes in your lineup the past two months based on his flaming start, you've had a .189 hitter with two homers over the last 162 PA. That's a player that is actively hurting you.
Rolling windows can be valuable when making start/sit or streaming decisions but should be taken as just one part of the bigger picture.
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