We've had numerous discussions here about Hafner's struggles last year and his possible future this season and beyond. One of the observations from his 2007 season was a significant increase in his GB% and corresponding decrease in his FB%. For a power guy like Hafner, who tends to hit the ball a long way when it's in the air, that's a bad thing. His LD%, while on the low end of his career, wasn't dramatically lower than it has been throughout his career. Here are his numbers for his career (LD%/GB%/FB%).
2002 19.10%/36.20% /44.70%
So Hafner hit 5% more groundballs than his career norm and about 4% fewer fly balls. Contrary to the argument that Hafner was still hitting the ball a long way (based on HR-distance), his HR/FB% was the lowest of his career at 15.9%. His career average in this arena is around 20%, and during his ridiculously good 2005 and 2006 campaigns it was at 24% and 30% (!). Part of this can probably be accounted for by luck (a recent article identified Hafner as one of the players with the fewest "cheap" home runs last year - those that just make it over the wall), but part of it may reflect not making the kind of solid contact we expect out of Pronk. Interestingly, Hafner's plate approach didn't appear to suffer. His BB% (15.8%) was the 2nd highest of his career and his K% (21.1%) was actually his lowest.
I posed the question the other day in one of the threads about whether or not there was precedent for players having single season significant departures in their ball in play (BIP) numbers and then rebounding back to career norms the next. I'm not a whiz at datamining the online baseball resources, but I did try to find some comparable players and look at what happened with them. Fangraphs, in addition to some fantastic new stats for pitchers (pitch type frequency, average speed), have BIP data for players going back to 2002.
Here are some of the comparables I found:
Manny Ramirez (2002)
I don't have Manny's 2001 data, but in 2002 Manny's GB% was 44.3%. His career average (2002-present) is 38.5%, so this was a pretty big departure from the norm for our former hitting savant. Same thing with his FB%, dipping to 30% from a career average of 39%. As it turns out, 2002 was a great year for Manny in Boston. Unlike Hafner last year, Manny's increase in GB% that season corresponded to a dramatic increase in HR/FB% (>30%) and accompanied a career high in LD%. So Manny's situation wasn't quite the same. But...for reference, the following season his GB% dropped back down to 35% and his FB% went right back to his career average of 39%.
Jason Giambi (2004)
2004 was the low point for Giambi. Injured for much of the year, he only played 80 games and put up a miserly .208/.342/.379 line. That season also saw his GB% jump from a career average of 31% to 40%. His FB% remained right where it's always been (~50%), but his LD% plummeted to under 10% (from an average of ~20%). Hafner says he wasn't hurt last season, so perhaps this is not a good comparison either. But again, Giambi saw his numbers rebound to his career norms (19%/33%/48%) in the 2005 season.
Andruw Jones (2004)
Andruw's 2004 season is the most comparable to Hafner's 2007 on the surface. His LD% dropped a few points, his GB% spiked by about 6%, and his FB% dipped slightly. This was accompanied by an overall drop in productivity (although his overall performance was in part driven by a spike in his K% as well). Jones wasn't injured as he played 154 games in centerfield that season. In 2005, Andruw's numbers rebounded back to his career norms.
Chipper Jones (2004)
The other Atlanta Jones also had a down season in 2004. Chipper, who is about as consistent as it comes year to year, saw a 5% jump in his GB% relative to his career norms, accompanies by a 6% drop in his LD%. His FB% was basically unchanged. These changes resulted in his worst season as a professional (.248/.362/.485). Chipper followed up the 2004 campaign with a far more Chipper-like season, with his BIP data returning to his career norm level.
Gary Sheffield (2003 & 2006)
Shef has seen two GB% spikes over the past 7 seasons, one which corresponding with his best season (2003) and one with his worst season (2006). The 2003 spike was accompanied by career highs in LD% and HR/FB%, perhaps making up for the increase in ground balls. Sheffield was injured for most of 2006, but when he did play, he wasn't the Sheffield opposing pitchers hate facing. He followed both seasons up with performances roughly equivalent to his career norms.
Jim Thome (2005)
This is another injury plagued season. Thome only played in 59 games for the Phils that season and wasn't terribly effective when he did. Healthy again in 2006 he went back to his old performance levels.
Alex Rodriguez (2004 & 2005)
This one's a little different. A-Rod moved to NY in 2004 having put up back to back seasons in Texas with ~20%/38%/40% BIP numbers (LD/GB/FB). His first season with the Yanks his LD% plummeted to 15%, his GB% jumped up to 45%, and his FB% stayed pretty constant at 39%. A-Rod's struggles (relative, that is) that first season with the Yanks is well documented. The follow-up 2005 season saw A-Rod put up similar ratios, but with a correspondingly better performance (his HR/FB% went back to a normal level and his infield fly numbers - which had skyrocketed in 2004 - came back to a more normal level). Since 2005 A-Rod's numbers have gradually been creeping back to his career norm levels.
So that's what I have. Not systematic, not thorough, and probably not very well thought out, but...a few observations. About half the guys on this list were injured and once recovered, recovered their normal performance. I would like to believe Hafner had some mysterious injury last season and is healthy now, but he himself says he wasn't. The others are divided between guys who balanced out a decrease in fly balls with an increase in line drives and therefore didn't lose any substantive performance levels, and the mystery guys like Hafner. The encouraging thing is that almost all of them did bounce back. A strange year, followed by a return to normalcy, is possible. We'll have to see what Hafner ultimately does this year, but maybe this can give us something to look out for.