No assumption in baseball is more sacrosanct than this one: Lefty batters hit righty pitchers better, and righty batters hit lefty pitchers better. Hundreds of major league careers, and literally millions of managerial decisions, have depended on the reliability of so-called platoon advantages.

So in a consideration of just how normal baseball is or isn't under pandemic rules, let's start with that steadiest truth: One-third of the way through the 2020 season, the hitter's platoon advantage is gone.

• Pitchers' advantage: .244 batting average, .738 OPS

• Batters' advantage: .238 batting average, .734 OPS

There has never been a season with anything close to a reverse split. The year with the smallest platoon advantage -- 1950 -- still saw batters produce about 10% more offense, or 35 points of OPS, when they had the edge. This year, through 25,000 plate appearances, it's a slight reverse split. If you crave normalcy, it's like a taunt.

This isn't the only way that some of baseball's core statistical trends are shaky this year. In the past century, the home team has won 54% of the time. This year, the home-field edge is nearly nothing: 50.6% through Tuesday, the lowest in more than a century. This year, batters are hitting .241 -- the second-lowest average ever, ahead of only the infamous "Year of the Pitcher" in 1968.

These are three relatively shocking developments, but they probably tell three different stories about this strange, memorable, discomforting season. The first one, about the evaporated platoon advantage, is probably just statistical mischief created by the short season's inherently small samples. The second one, about the collapsing home-field advantage, is a potentially illuminating revelation on how much home-field advantage is about the influence of fans in stands -- though it might also be about the small sample. The third, about the low batting average, might be the small sample, might be about the lack of fans, might simply be a continuation of Normal Baseball trends that had already been pushing averages lower, or might be something else.

Saying what it all means is harder than ever, and there's a question at the heart of it that's especially hard to answer:

What exactly are we watching this year -- and is it any good?

As I've watched baseball this year, I've been keeping a little log of everything pandemic-related that could be affecting how good the ballplayers are performing. This isn't about things like the composition of the ball, which can tilt the edge toward pitchers or hitters but doesn't affect anybody's actual talent. I'm talking about things that would cause the median major leaguer this year to be better or worse. There are several dozen, some of which seem likely to raise the quality of play we see, some of which would hamper it.

The Grind

1. Players will travel, on average, only about 8,000 miles this year, or about 130 miles per game. Last year, they traveled 34,000 miles per team, or 210 miles per game. A 2017 study found that jet lag impaired both offensive and defensive performance at the major league level, but this year few teams will have to hop more than a single time zone. The Brewers' total travel is only longer than a single flight from Seattle to Miami would be.

2. The season will be considerably shorter, which -- in theory -- allows managers to use their better players more often, without having to worry about the cumulative effects of innings totals and the summer grind. To give one example: In 2019, there were 39 players who started every one of their club's first 16 games, 10% of that season. This year, there are 53, not counting any Cardinals (who haven't played 16 games).

3. The season will be considerably shorter, which reduces the actual effects of the grind itself. In 2014, Baseball Prospectus' Russell Carleton found the physical and mental strain of a long season really did cause players to get worse in later months, as measured (by Carleton) in a loss of plate discipline. Every player this season is, in theory, going to be relatively fresh to the end.

4. However, the season is also considerably more condensed this year. Every team has fewer off days, on average, than in a normal summer. And after the Marlins and Cardinals saw entire weeks of their schedule wiped out by positive COVID-19 tests, they're now scheduled to set records for most games played in the fewest days.

5. Teams also had a shorter preseason immediately before the season began, which would mean less grind but also less preparation. Some of the early part of the season was likely spent just catching up.

Who Is Playing

6. A dozen and a half major leaguers have opted out of this season, for health and safety.

7. Dozens have missed time after testing positive for COVID-19, including about 2% of all players at the beginning of preseason camps. At least 27 Marlins and Cardinals tested positive after the season began. MLB requires players who test positive to sit out at least 10 days, but for many the illness has taken much longer to recover from. Not all players who tested positive before the season have returned, or will.

8. With no minor league baseball, scores of players who would likely have played their way onto major league rosters over the course of a 2020 season are instead inactive, and clubs' depth is limited to 60 total players. The nonactive players are at alternate sites, playing, but not exactly in the routine of daily, intense games: "Because the alternate site has a maximum of 30 players, some games wind up with staffers playing positions," Jeff Passan just wrote. "There are not enough arms to stage daily nine-inning games, either."

9. There's been a huge spike in pitcher injuries this year. That's likely a combination of two things: the typical start to the season (which historically produces a swell of arm injuries) and the atypical start to this season, with a spring training in March followed by a long layoff followed by a second, short preseason camp in July and then Opening Day.

10. When players come back from their injuries (or illness), there aren't any competitive minor league games for them to make rehab starts in. That could affect stamina for pitchers, as when Stephen Strasburg returned from nerve issues in his throwing hand and hit a wall after about 40 pitches in his first start. It could affect hitters' timing: Even hitters who do get rehab at-bats show some rustiness from absence, which could only be made worse by a lack of minor league games.

The Setting

11. There are no fans cheering. If some part of home-field advantage is about players feeling encouraged by cheers, that's missing this year. And it could well be that the energy of fans makes both the home team and the visiting team better. (That's just speculation. It could also be that empty stands help players stay calm. Or, likely, that different players react differently to the presence of fans.)

12. There are no fans in the backdrop. The Ringer's Ben Lindbergh suggests this as a hypothesis for why batting average is down: Without fans' multi-colored wardrobes, defenders might be picking the ball up off the bat better. Without fans' noise, they might even be hearing the crack of the bat better. The Wall Street Journal's Ben Cohen and Joshua Robinson found that NBA players are making more corner three-pointers and free throws this year, suggesting a similar "backdrop" effect in other sports.

The Competitive Drive

13. More teams are "in it." On Aug. 18, 2019, there were 16 teams whose playoff odds were in the single digits. This year, with the short season and the expanded playoffs, only three teams' playoff odds were that low -- and even those three teams were no more than six games out of a playoff spot, putting them within a winning streak of October. That gives nearly every team motivation to try every night.

14. There are few statistics to chase. Almost nobody is setting any career highs in home runs or strikeouts this year, and the traditional benchmarks of individual achievement (100 RBIs, a 30/30 season, a record chase) are out of reach. There's some evidence that players actively "target" and are motivated by round-number milestones, but those aren't available this year. And for some players, "bad" seasons are already all but guaranteed, with a third of the season complete. It's already all but certain that this year will be an underwhelming blip on the statistical line of Jose Altuve or Madison Bumgarner's career page.

15. But, if there's less competitive drive this year, there's also less pressure. Not one player will be booed on his way to the plate, and every underwhelming blip on a career line can be dismissed as "the COVID year."

The One-Year Rules Changes

16. There's the universal DH. It isn't as though there were 15 Nelson Cruzes waiting around for an NL team to hire them, and the 15 "new" designated hitters in the NL have collectively hit only about .220/.300/.400. But that's nearly infinitely better than what pitchers normally hit -- .130/.160/.160 -- in about 5,000 plate appearances a year, and also superior to the .650-ish OPS that batters pinch hitting for pitchers usually hit.

17. There are shortened extra innings and 28-man rosters. Removing the threat of a 16-inning game lets managers empty their benches and bullpens a bit more liberally earlier in games. To give one example: Teams have used at least two catchers in a game 80 times, about twice as often as they did last year. Starting position players at all positions have been replaced more often this year than in any of the past 10 years, and even with the shorter games there have been more relievers used per game. Those could mean different things, but one possibility is that managers have more options and tactical flexibility to get their best players in the game for each situation.

The Mood

18. There are no high-fives -- or a lot fewer. At least some part of a player's motivation must come from the positive responses he gets from the group he identifies with. There are fewer butt pats to go around this year.

19. There is a lot less time spent hanging out in the clubhouse, bonding with teammates. As Russell Carleton has written, "We should think of [clubhouse] chemistry as the answer to the question, 'Why should I bother?' There will always be a time when you just don't want to, and the answer is going to have to be 'because my teammates are counting on me and I don't want to let them down.'" If we believe in the power of clubhouse chemistry, then it implies some skill is lost by our social distancing this year. (There's also less opportunity for players to share observations with each other.)

20. There is all the same lack of social support that many of us have: They can't go out at night, they worry about their kids losing time with friends. A lot of them probably haven't seen their parents in months.

A lot of them are probably dealing with clinical depression or anxiety.

A lot of them are probably in grief, and wonder constantly about the value of performing something frivolous in the middle of national mourning.

You could wonder for hours about how other, smaller things might matter. The corner outfielders don't have a ball boy to warm them up between innings this year. That can't matter much -- can't really matter at all, right? -- but they must do it for a reason, and now they can't. Who knows what spitting and throwing the ball around the horn and sitting next to a teammate while watching the game are worth?

"It doesn't pass the sniff test for real baseball," a front office analyst told The Ringer's Lindbergh, but that seems hyperbolic. Statheads will try for years to figure out precisely and specifically how the pandemic affected play, but for the most part all of these crisscrossing pressures haven't lowered the level of play in a clear, obvious, obnoxious way:

The average four-seam fastball is 93.3 mph, comparable to last year's 93.4 mph average. Four-seamer and slider spin rates are up slightly. Hitters' exit velocity is down slightly from last year, but within the range of the past five years, and by other measures of quality contact, 2020's hitters have been typical. Defense, as measured by percentage of batted balls turned into outs, has been better than it has been in recent memory.

Pitchers have probably been a little wilder. The league's rate of strikes is 63%, down from 64% -- though that could be wilder pitchers or it could be more selective hitters. When they've had to throw a strike -- in 2-0, 3-1 and 3-0 counts -- they've thrown slightly fewer pitches in the zone, but only slightly. And batters have probably been a little worse, too. When they swing at pitches down the middle, they're whiffing slightly more often this year -- on 14% of swings, up from 13%. Taken together, the league is probably slightly less talented this year. But so are we all.

Major League Baseball always changes. Over the past century, the style of play has changed in some ways, stayed the same in others, gotten more extreme or doubled back on itself. Chart it, and almost any measure of Major League Baseball looks like one of two stories:

Or

In the first -- strikeouts per game -- a line goes up and up and up and might never stop going up. The ability to strike batters out is the core skill of pitching, and decades of pitcher development, scouting, physical training and technique are geared toward throwing the ball harder so as to strike more batters out. The line reflects progress.

In the second -- runs per game -- a line goes up and it goes down, often in hunks of years. Scoring turns out to be sensitive to environmental changes: ballpark designs, the constitution of the baseball, the number of teams in the league, even things like weather. The line is always moving in response to the environmental conditions but, for the most part, always gets back to its fairly narrow range. That's the game's central balance between pitching and offense. It can't get too out of whack, or it stops seeming fair, stops seeming like baseball. Various forces naturally keep this balance in line, and when that fails the league steps in to do it. The line reflects balance.

We should be prepared for this year to be an anomalous blip in a lot of those charts. Walks are up this year, higher than they've been in two decades. Hit by pitches are higher than they've ever been in history. Doubles are less frequent than they've been in any year since 1991, and they aren't turning into triples -- those are lower than any year in history. Intentional walks are lower than any year in history. Batting average on balls in play is way down, for some reason. Center fielders are playing deeper this year, for some reason. Time of game is up, for some reason.

Those all might be continuations of trends, or they might be caused by the pandemic, or they might be caused by our responses to the pandemic, or they might be simple weirdnesses that can show up in any three weeks of any baseball season.

On Tuesday, in the 10th inning, the Twins brought left-handed reliever Caleb Thielbar in to face left-handed hitter Ben Gamel. The Brewers responded as teams have always responded: They pinch hit for Gamel with a right-handed batter, Orlando Arcia. There isn't a manager in the world who believes that 100 years of platoon advantages have suddenly gone poof because of a virus. This season might be weird, but at its core is a belief that normal still exists, and if we're not living in it right now we might still hold out hope that it will come back soon. Arcia flied out.