Hitters usually have a fairly linear development path. Pitchers may invent a new pitch or adjust their mechanics and in the process transform themselves from year to year, but hitters progress more steadily, evolving by steady degrees. Once a hitter has established himself as a regular in the major leagues, it is unusual to see them suddenly regress to the point that, after a period of years and/or a substantial number of games, they have to be sent back to the minor leagues for reeducation. Yet, that is exactly what has happened this season with two notable players, center fielder Chris B. Young of the Diamondbacks and shortstop J.J. Hardy of the Brewers.

Young arrived in the majors in August, 2006. In his rookie campaign the next season, he hit 32 home runs while striking out 141 times against just 43 walks, leading to .237/.295/.467 rates. His sophomore season was substantially similar, though Young dropped 10 home runs despite adding 75 plate appearances over the previous year. This year, the wheels came off entirely; Young batted .178/.220/.313 through the end of May, enjoyed a brief .246/.402/.508 surge in June, then crashed again, batting .184/.339/.333 in another month’s worth of games. He has hit just one home run in his final 100 at-bats. Young was sent down on August 10, just shy of his 1800th plate appearance in the majors, as well as his 26th birthday.

Hardy turns 27 tomorrow, but he got the same present for his birthday as Young. He became the Brewers’ starting shortstop in 2005. An ankle injury curtailed his 2006, but he broke out in 2007, batting .277/.323/.463 with 26 home runs. He solidified his progress in 2008, batting .283/.343/.478. Flipping the calendar to 2009, Hardy struggled in April, but heated up to .300/.400/.488 in May. Instead of building from there, he slumped, batting .224/.288/.350 into August. In danger of sliding out of the pennant race and hot prospect Alcides Escobar pressing from below, the Brewers demoted Hardy, veteran of 558 major league games, on August 12.

Over the last few years, the reeducation trip has become increasingly common, as the pressure of multi-million dollar payrolls has limited teams’ patience with slumping twentysomethings, even if their veteran status would seem to grant them the benefit of the doubt. In 2008 it was the turn of the BravesJeff Francoeur, despite having played in every game in 2006 and 2007. Though he struggled with plate discipline, his strong second half in ’07 seemed to portend a major breakthrough. Instead, Francouer quit hitting altogether. After 85 games he was batting .234/.287/.374. The Braves sent him to Double-A Mississippi to rework his swing. He played in only three games, going 7-for-13, before injuries in the majors demanded his recall. Francoeur wasn’t much improved upon his return, batting .245/.303/.340 in his final 70 games, and began this season hitting .250/.282/.352 in 82 games before being dealt to the Mets.

The Yankees had their own slumping outfielder to deal with last year. After two seasons of mediocre hitting as a regular for the Yankees, first in left field and then in center, Melky Cabrera hit .299/.370/.494 with five home runs in April. That was largely it for the season, as he batted .226/.274/.293 over the next 90 games. Seemingly complacent and a bit out of shape, he was sent down in mid-August. Cabrera hit well in the minors, carried that success over in a September return to the Bronx, and was enjoying his best season in 2009 before a recent cold snap.

In 2007, Rickie Weeks of the Brewers received the grand tour. Weeks played regularly in the majors in both 2005 and 2006, but wrist injuries prevented him from staying in the lineup and achieving consistency. In those two years he played 191 games and hit .259/.348/.399 while spending significant time on the disabled list. Weeks got off to a decent start in 2007 (.245/.345/.432 through May) but pain in his surgically repaired right wrist again forced him to the sidelines. When he returned, he was completely unable to hit, batting .149/.229/.223 over the next six weeks. The Brewers sent him down. Weeks played just six games at Triple-A Nashville, but went 10-for-22 and drew five walks (.455/.571/.682). Upon returning he was finally what the Brewers had dreamed of when they selected him the second overall pick of the 2003 draft, batting .273/.442/.553 with 11 home runs over his final 43 games. Unfortunately, the lesson didn’t carry over to 2008, when Weeks again struggled.

On the whole, these players don’t have much in common. Francoeur’s insistence on hitting his way on base is almost pathological, while Weeks’ early career was greatly affected by injuries. Cabrera was never a great offensive talent to begin with. Young’s difficulties in making solid contact-he is one of the more prolific hitters of pop-ups in the majors-hinted at some essential flaw in his approach, though not one that would undo him to this degree. Hardy’s slump seems like just one of those things.

More broadly speaking, all of these players are limited in ways which require them to perform perfectly or lose productivity. None are high-average hitters at the best of times, which puts pressure on them to walk or hit home runs and generate offense in other ways. More rounded hitters have secondary skills on which to fall back. These players largely do not, and it makes their slumps much more difficult to endure.

Young has played only three games at Triple-A Reno, but has done well, going 6-for-14. Hardy has also played three games, going 1-for-9 with a home run. Neither line is significant. What is more important is isolating the nature of their scuffling, be it mechanical, physical, or psychological. The reeducation trip might get them sorted out, but as recent experience shows, it is unlikely to erase their limitations.

A version of this story originally appeared on ESPN Insider Insider.