The Kia Tigers are doing a lot of things right. At 64-34-1, they are in first place in the Korean Baseball Organization, with a comfortable five-game lead over the second-place NC Dinos. As a team, they are slashing a cumulative .306 / .375 / .479, and are first or second among teams in the KBO in virtually every offensive category.

But the emphasis on offensive firepower has not come at the expense of pitching; while Kia’s hurlers are not dominating the league the way their hitters are, their pitching staff ranks first in the KBO in WAR (15.8), and has above-average marks in ERA+ (105) and FIP+ (105.6). This is a solid, well-rounded team.

However, Kia has had one major flaw throughout the season: They play significantly worse on the weekends.

The KBO schedule is set up such that each team plays two three-game series per week, one from Tuesday to Thursday, and one from Friday to Sunday. Throughout the 2017 season, Kia players, both pitchers and batters, have performed significantly worse on the weekends. The effect is most noticeable on the hitting side, with a precipitous drop in performance in games that happen in the second, Friday to Sunday, series of the week.

The table below shows the batting splits for the top-10 Kia hitters (by plate appearances), as well as the team as a whole, and clearly shows the distinction between the mid-week and weekend series. From Tuesday to Thursday, Kia hits like, well, Kia. But from Friday to Sunday, Kia’s cumulative batting line is comparable to that of the Lotte Giants and Samsung Lions, who are in seventh and eighth place, respectively.

This stark difference in team performance has borne out in the team’s record. On Tuesday to Thursday games, Kia is 41-9, an .820 winning percentage, or an 118-game-winning pace over a full 144-game season. For comparison, the KBO single-season wins record is 93, set by the 2016 Doosan Bears, and the 90-win mark has only been eclipsed one other time, when the now-defunct Hyundai Unicorns won 91 in 2000.

However, on Friday to Sunday games, Kia is 23-25-1, a .469 winning percentage, or a 68-game-winning pace. If Kia had a .469 winning percentage this season, they would slot in at eighth in the standings between, guess who, Lotte and Samsung.

There are no clear reasons for this drop-off. Kia’s schedule has been fairly balanced between the weekday and weekend series, and they have faced good and bad teams alike. Other teams have some variation between weekday and weekend, but there is no league-wide trend toward weaker weekends, and especially no performance gaps as severe as Kia’s.

However, as Kia is still well in control of the 2017 KBO standings, and performing well overall, this weekend drop-off stands as more of a curiosity than an actual problem. Perhaps it actually makes the team even scarier; despite running roughshod over the rest of the league, the Kia Tigers still have room to improve.

A lot of things have clicked for the Kia Tigers this season, chief among them being their offense’s record production. Kia’s fearsome lineup features three of the Korean Baseball Organization’s top-10 hitters by batting average, and five of the top-20 hitters by wRC+, and is a driving force behind the team’s domination of the standings, currently sitting in a comfortable 1^st place at 64-34-1, five games up on the second-place NC Dinos.

A major force behind the dominance of the Kia offense has been the unexpected emergence of their new center fielder Roger Bernadina, in his first season in the KBO. Just a season ago, Bernadina was toiling in the minor leagues, playing with the Las Vegas 51s, the New York Mets’ Triple-A affiliate.

The difference between the old Bernadina, a failed prospect who played seven partial seasons in Major League Baseball, mostly with the Washington Nationals, and the current Bernadina, who hits leadoff for the Kia Tigers’ offensive juggernaut, is stark.

In less than a fifth of the games played, Bernadina has already accumulated over three times his MLB WAR and hit over half as many home runs (19 to 28). By wRC+ he has been the 16^th most productive player in the KBO this season, and by WAR, he has been the 6^th best position player in the league. On Thursday night he hit for the cycle, becoming only the third foreign player to do so in the KBO. Quite a jump for someone who was a career 81 wRC+ hitter in the MLB.

Which of course begs the question: What’s changed? In less than a season, how has Roger Bernadina improved this much?

It isn’t plate discipline; Bernadina is actually walking slightly less (7.7 percent in the KBO versus 8.2 percent in the MLB) and swinging more (50.3 percent vs 42.1 percent). His strikeouts are down from 21.3 percent in the MLB to 17.4 percent in the KBO, but that change may be more a function of the leagues themselves (the MLB’s higher overall K% means Bernadina’s mark is about league average in both leagues) than any adjustment Bernadina himself has made.

Bernadina also still profiles as the same type of hitter, hitting a majority of his batted balls on the ground, with a moderate preference to pull. He never displayed particularly drastic platoon splits, hitting roughly the same against lefties and righties, and this tendency is also unchanged. Though his batted-ball characteristics would have made him a reasonable shift candidate, shifts were almost never employed against him in the MLB, so his increased numbers in the KBO are also not the result of the KBO’s relative lack of defensive shifts.

The biggest difference is the change in Bernadina’s batting average on balls in play. His current KBO BABIP is .353, a drastic increase from his career MLB BABIP of .288.

On one hand, Bernadina profiles as the type of hitter than might naturally run a higher BABIP. He runs well, having rated as a positive baserunner and base-stealer in both his time in the MLB (59 steals, 83% success rate, 8.9 BsR) and the KBO (21 steals, 81% success), and the fact that he is primarily a ground-ball hitter should give him ample opportunity to take infield hits and run a higher BABIP.

However, his track record shows this to not be the case. BABIP is a statistic that takes a long time to stabilize, and as such his career average is more indicative of him as a player than his current 2017 outlier mark. With no other changes in batted-ball profile or batting approach, Bernadina’s increased BABIP, and by extension increased offensive production, is more likely the result of fortunate circumstances and luck than any real change in skill.

That being said, simply acknowledging that Bernadina has been lucky this season does not diminish his performance. Regardless of whether he is performing to his expected outcomes or not, he has been a productive member at the top of the Kia Tigers’ lineup and, perhaps even more interestingly, has hit better as the season has progressed.