Bryce Harper had an offensive season for the ages in 2015. With a wRC+ of 197, he put himself 24 percentage points (pp) above second-place Joey Votto. In 146 seasons of major league baseball, only 32 times has a player put at least that much distance between himself and the next best hitter in the league. In the twelve years since Bonds was colluded against retired Harper is the only player to do it. Bryce Harper had arrived, and the precocious star seemed poised to dominate for the foreseeable future.

But then, a funny thing happened. Not the type of funny that leave you in stitches, holding your stomach, but instead holding your head, questioning everything that you thought to be true just six months earlier. He entered the season a lion, but transitioned to lamb status after about a month. When it was all said and done, Harper’s 2016 wRC+ sat at a pedestrian 112, 85 pp lower than the previous season.

Over the course of their entire careers, only 2 percent of players who have qualified for the batting title at least twice have seen this much difference between their best and worst seasons, but that includes nearly every player that has posted a wRC+ greater than 190. From that perspective, Harper’s 2016 doesn’t look so bad.

But for many of these players, steady periods of excellent production are book-ended by their average or even slightly below-average years, Harper’s worst season came right on the heels of his best season ever, and one that was widely seen as him cashing in on his potential and joining the games’ elite.

Adjust the query to sort by difference in wRC+ between consecutive years where the hitter qualifies for the batting title, and the decline between Harper’s 2015 and 2016 shoots up the list, ranking as the second-largest ever. That’s not the in modern era, or since the mound was lowered, or since any one of numerous expansions to the league. That’s since 1871, season zero on FanGraphs and Baseball-Reference, ever.

But second-worst isn’t worst, right? Well in this case, it almost certainly is. And to find out why, you need to consider the circumstances that surrounded the greatest decline in major league history.

WARNING: Gory historical details ahead!

In 1883, the two major leagues, the National League and American Association, signed the National Agreement, which prevented teams from the either league from signing certain players away from the other. This formalized the reserve lists, which had previously been covertly shared among National League teams, but also expanded the number of players a club could protect from five to eleven.

Moral opposition to the reserve clause spurred the creation of another so-called major league, the Union Association, by Henry V. Lucas, a prominent St. Louis businessman and baseball fan. Union Association teams would not recognize the reserve lists of the other leagues, and its teams were free to sign any player not under contract. Prior to the inaugural 1884 season, Lucas scooped up Fred Dunlap, the star second baseman of the National League’s Cleveland Blues.

Dunlap was perhaps most renowned for his defense, which earned him the nickname Sure Shot, but he was no slouch at the plate either, as Dunlap established himself as roughly 30 percent better at the plate than league average over his first four major league seasons. However, in his fifth season, now with the St. Louis Maroons of the upstart Union Association, the goal posts for league average changed drastically.

While the Maroons succeeded in putting together a talented team, the rest of the Union Association did not. It was a tumultuous season for the fledgling league that saw half of the teams in the fold be replaced by teams from lower leagues and even a brand new franchise. By the end of the season it was clear that the Maroons, led (literally) by Dunlap, who was a player manager for most of the games, were head and shoulders above the rest of the league, with an average run differential of 4.0 runs per game.

Dunlap himself was hands down the best position player in the league and he finished the season with a wRC+ of 214, the fourth largest increase (78 pp) in consecutive seasons. Dunlap distinguished himself to this extent because wRC+ compared him to his peers, who were worse in the Union Association than any year he would play in the National League. For that reason, Fred done lapped the field, creating 114% more runs than average, which also happens to be greater than any other major league season in the 19th century.

The Union Association lasted just a single season, after which the Maroons, along with Dunlap, joined the National League. In 1885, Dunlap posted a wRC+ of 118, 96 pp lower than the previous year, good for the most precipitous decline on record. But by playing in a league of dubious talent, that may not even have been considered to be part of the major leagues until 38 years after it disbanded, Fred Dunlap’s 1884 season shouldn’t be included in the records.

Of course, the baseline for league average offense did not change, at least not to the same degree, for Major League Baseball between 2015 and 2016. Yes, the offense was up by 5 percent, home runs were up by 14 percent, and the distribution of wRC+ was clustered more closely around the mean, but the composition of the talent pool that Bryce Harper joined was not fundamentally different in the way it was for Dunlap in 1884.

It’s difficult to untangle regression, bad luck, and injury when trying to explain any decline, or improvement, in player performance. But what we do know is that the decrease in offensive production from Bryce Harper is the greatest we’ve ever seen in the history of the the major leagues, at least if you agree with Bill James that the inclusion of the Union Association in major league records is “farcical”.

Luckily for the Nationals, they had Wilson Ramos, one of the forty players to gain at least 60 pp of wRC+ in a single season, to offset some of Harper’s decline. Well, thirty-nine players, if you drop Fred Dunlap.

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Matt Jackson is an occasional writer for Beyond the Box Score. You can follow him on Twitter at @jacksontaigu.