CHICAGO -- Gary Sheffield says he feels his best in terms of health since he hit 21 home runs over the first half of last season. His feelings about balls and strikes lately are another matter.

"It's terrible," Sheffield said of the strike zone. "Worst I've ever seen. And pitchers know it."

Sheffield has made his living over the years as one of the game's rare hitters who combined batting average, power and walks. He entered Thursday's series finale against the White Sox ranked fourth among active players with 1,415 bases on balls and eighth with 489 home runs. With the exception of an injury-plagued 2006 season in New York, he has had more walks than strikeouts in every season since 1994.

That streak is set to come to an end this year, with 38 walks and 58 strikeouts so far. Part of the problem, of course, was a different approach he had while he was still hampered by his shoulder, forcing him to start his swing sooner. However, Sheffield also railed Thursday against what he sees as a more generous strike zone than in past years.

It's so generous, Sheffield said, that he has changed his approach.

"When I go to hit, I don't think about getting a walk," a clearly frustrated Sheffield said. "I don't think about [not] swinging until they throw a strike. I think about swinging when I can get to one. You have to really walk me, because I'm not trying to walk anymore. And that's exactly why I'm hitting .220."

Sheffield entered Thursday batting .228, an average that has risen just slightly since he began feeling healthier. He's hitting .268 (11-for-41) over the last two weeks with two homers, eight RBIs, four walks and nine strikeouts.

The specialized statistics are mixed. According to research on baseball-reference.com, one-third of Sheffield's strikes this season have been called strikes, tied for the highest percentage in any season of his 21-year Major League career. His next called third strike will tie his total from all of last season despite almost 200 fewer plate appearances. Meanwhile, he has swung at the first pitch in just 13 percent of his plate appearances, the lowest mark of his career.

Manager Jim Leyland gave him Thursday's game off with the idea of resting him. It's also part of Leyland's plan of rotating his outfielders in and out of the lineup to give them all something close to regular playing time.

The relationship between Sheffield and umpires' strike zones has long been tumultuous. He was suspended last summer after home-plate umpire Greg Gibson accused Sheffield of tossing his bat at him after arguing balls and strikes on his way to first base on a groundout, a charge Sheffield vehemently denied.

So far this season, however, Sheffield has kept a very low profile at the plate. By his unofficial count, he has had words with an umpire twice this year, but nothing heated.

"I haven't come close," Sheffield said. "I tell myself before I walk out that I'm not going to say anything. They can do whatever they want. I don't care. I'm not going to sit here and go through trying to defend myself for disputing anything about an umpire. They can call it how they want. If I strike out, I strike out."

Those pitches on the corners, Sheffield said, have become more frequent since he began feeling better. Pitchers would challenge him over the plate when his shoulder wouldn't allow him to catch up.

"You're in a spot where you just take it like a man," Sheffield said. "You know you're just limited in certain areas and they were throwing you little lollipop curveballs up there, knowing you couldn't reach them. Now it's a different ballgame. Yeah, you might get me out on certain pitches, but I'll tell you what, you're not going to get me out over the plate.

"If umpires aren't giving pitches off the plate like they have been all year, and pitches in off the plate like they have been all year, then they don't have anywhere else to go."