It is a rare hitter that performs at exactly the same level two straight years. Some guys do alot better one year than in the previous year, some do worse. I look at the biggest gainers and losers the past two years using a Bill James stat called "offensive winning percentage."
Offensive winning percentage (OWP) is suppose to tell us what the winning percentage would be for a team of 9 identical hitters if it allowed an average number of runs. Since I used data from Lee Sinins' "Complete Baseball Encyclopedia," the numbers are also park adjusted. Using OWP is better than using HRs, RBIs, batting average, etc. since it boils all of hitter's value down into one single number. I looked at all hitters who had at least 300 plate appearances in both 2005 and 2006. There were 212 such players.
The table below shows the 26 biggest gainers.
Corey Patterson saw his AVG-SLG-OBP rise from .215-.348-.254 to .276-.443-.314. He actually had a .576 OWP back in 2003, so last year was a nice comeback for him. The move to Baltimore must have done him some good. Justin Morneau, MVP of course, has been considered a prospect. He had an OWP of .598 in 2004, but it fell to .434 in 2005 (pretty bad for a 1Bman). So this year's gain means he finally fulfilled his promise. Carlos Beltran took a step towards becoming a super star after a disappointing first year as a Met after signing a big contract. He was over .600 in both 2003 and 2004 (.683).
The rest of the top 10 are generally young or inexperienced players who had break out years. Same for Ryan Howard, Robinson Cano, Freddy Sanchez and Nick Swisher.
Scott Hatteberg and Vernon Wells are more or less veterans returning to form after poor seasons. Jermaine Dye is somewhat unusual in having his best year at age 31. It is a good bit better than his next best season in 2000 (.658), which was his only other year over .600.
The table below shows the 25 biggest losers.
Rondell White, Reggie Sanders, Ken Griffey Jr., Jason Varitek, Brian Giles, Javier Lopez, Brad Ausmus, Craig Biggio, and Matt Stairs will all be 35 or older as the 2007 season gets under way. At their age, we have to wonder where their careers are headed.
Placido Polanco is only 31 but he was .100 below his career OWP. His OWPs from 2003-5 were .552-.501-.614. So 2006 was pretty disappointing. Brian Roberts pretty much just returned to normal. His career OWP is .518. He had .472 and .453 in 2003 and 2004. Mark Ellis has been all over the map. In his 4-year career he has had .512-.434-.628-.409. Angel Berroa is a young player on a very bad downward path. His OWPs the last 4 years have been .466-.400-.388-.172. Bobby Crosby is young, too, and inconsistent with OWPs of .411-.535-.320. Randy Winn had an off-season. His career OWP is .506. His OWPs from 2002-2005 were .609-.553-.535-.618. Coco Crisp had a surprisingly bad season given that he was .515 and .606 the two previous years. Travis Lee had the worst year of his career, far below his career OWP of .462.
Jhonny Peralta, Jonny Gomes, Jorge Cantu are young players who have just had 1 bad year and could bounce back. Maybe one of them will be the Justin Morneau of 2007.