"Trevor Hoffman didn't hesitate when asked the question.

What's the key to a good changeup?

"Fastball command," said Hoffman. "You can't be throwing a lot of changeups when you're behind in the count. Hitters are going to take it."

If anyone knows how effective a changeup can be, it's Hoffman.

The Milwaukee Brewers' new closer punched his ticket to Cooperstown as the all-time saves leader (554 entering 2009) by throwing an endless stream of changeups to hitters.

The hitter knows it's coming. The opposing bench knows it's coming. Heck, the peanut vendor knows it's coming.

Yet, far more often than not, the pitch works for Hoffman, not to mention other changeup specialists such as Philadelphia's ageless Jamie Moyer and young teammate Cole Hamels as well as Chicago White Sox lefty Mark Buehrle.

Not coincidentally, the changeup was a focus of the Brewers' training camp this spring under manager Ken Macha. On the very first day he gathered his pitchers, pitching coach Bill Castro emphasized the importance of having a dependable changeup.

"I believe in the changeup as a big part of pitching," said Castro. "Good pitching is destroying a hitter's timing. You command your fastball on both sides of the plate, then use the changeup.

"If you throw it for strikes, then you can get the batter with a fastball. It looks so much like a fastball when you're throwing it right. When you're aiming it, you give it away. And you have to have the confidence to throw it in any count."

Arm speed a factorThe key to fooling a hitter with a changeup is having the same arm speed as your fastball. The hitter thinks it's coming faster than it actually is and gets out in front of the pitch, missing it, popping it up or grounding out weakly.

To succeed, you must have separation in the speed of your fastball and changeup in the 7-10 mph range. If you throw your changeup too hard, it in essence becomes a "batting practice" fastball and often is launched into another galaxy.

"It's not how hard you throw your fastball," said Castro. "It's the difference in speeds (between fastball and changeup). Moyer gets you out with location of the changeup, the fastball and the 'cutter.' He gets everybody out front. They're looking for it but when he throws it right, it doesn't matter.

"Hitters know Hoffman is going to throw his changeup. If it's thrown the right way, it's tough to pick up. It has the fastball rotation. You're looking for the fastball and you get out in front."

Because it is the difference in speeds that makes for a good changeup, you don't have to be a hard thrower to fool hitters. Moyer barely cracks 80 mph with his "heater." Hoffman often throws his fastball in the low to mid 80s.

"It's not fun to go out there and 'man up' with a 73-mph pitch," Hoffman said with a laugh. "There's definitely some cat-and-mouse involved that you get into.

"You're always changing. When you see your fa