Most disappointing 2011 seasons

There's nothing unusual about getting off to a bad start. When a star begins the season poorly, people rightfully shrug and figure that the player will eventually start playing at his normal level. But as April turns into May and May turns into June, the doubts start to speak a bit louder. We're more than a third of the way through the season, and while going into full-blown panic usually isn't warranted, one does need to adjust expectations downward for a player who is still scuffling.

Not all bad seasons are created alike, though. For example, changes in walk and strikeout rate are far more likely to be retained going forward than changes in batting average on balls in play (BABIP). A homer outage for a home run hitter is a greater cause of concern than a singles hitter having a single outage.

So, which full-time players with worse-than-usual season lines should we be most concerned with? With the aid of the ZiPS projection system, I found the hitters and pitchers whose poor years have most negatively affected their short-term and long-term performance. For each player, I've included their projection from before the season and their expected projection for the rest of the season (BA/OBP/SLG for batters and ERA for pitchers).

Hitters

5. Adam Dunn -- Preseason: .252/.383/.539, Update: .235/.369/.490

There were good reasons going into the year to expect Dunn to do well in Chicago. While Dunn has always displayed what Bill James referred to as old players' skills -- walking and hitting homers -- he's only 31 and had hit 38 or 40 home runs in every year going back to 2005. U.S. Cellular Field is the best homer park in the AL and it seemed custom-fit for the former Nationals slugger. Instead, it's June and he has a slugging percentage worse than Juan Pierre. Dunn will end the year with an OPS better than .623, but the odds are that we're seeing the start of his decline.