Base stealing is part art and part science. The Astros' Michael Bourn uses a little bit of both qualities to be one of the best in the Major Leagues at this complicated task.

At the end of August, Bourn had 146 stolen bases since the start of the 2008 season, tops in the Majors. He stole 61 bases last season to lead the National League and was well on his way to another base stealing crown this season with 44 in the last weekend of the month. His 32 infield hits also led the league.

There is no one-size-fits-all technique to swiping bases, according to Bourn. "A lot of it depends on the pitcher," he said. "How long has he been in the league? Does he have a high leg kick? What's his rhythm?"

Learning all that requires doing homework. Bourn does his on pitchers, and he knows opposing teams do theirs on him.

Does he bring a plan with him when he reaches base?

"I'm unlikely to go on the first pitch unless I know you," Bourn said. "It's a little bit of a cat-and-mouse game. They have reports on me, and we have reports on them.

"A lot of it is anticipation. The first three steps are the most important part. If you get a good jump and know how to run, you're in good shape.

"Pitchers vary. You might get one pitch to run on, just like you sometimes get one pitch to hit. You can't miss that pitch. That split second makes all the difference between making it and getting thrown out.

"Sometimes, I don't get a good jump. Speed can make up for that. I know when to go. Sometimes, they might focus on me but not all the way. If they do, it takes away from their focus on the hitter, and that helps us. If they focus on the hitter, that helps me."

Bourn was in the middle of a four-game Astros' sweep of the Phillies at Citizens Bank Park, going 8-for-20 with four stolen bases and four runs scored. One of the runs came on a dash to the plate after an infield out when he beat Ryan Howard's throw home. Daring baseball is a Bourn specialty. "If there's a chance," he said, "I'll take the risk."

Bourn came to Houston in a 2007 five-player trade that sent closer Brad Lidge to the Phillies. It was a chance to go home for the Gold Glove outfielder who grew up in that city and was drafted by the Phillies after he spent three years at the University of Houston.

Still, he was shaken by the deal.

"I was shocked when it happened," Bourn said. "I had been with one organization from the time I was drafted. It was all I knew. I had fun there. I enjoyed it. And then came the trade. But then I thought, 'Hey, I'm going home.'"

It also meant he would have an opportunity to play more. The Phillies' outfield was crowded and the trade meant Bourn would have more of a chance at regular work. "At first, there was some pressure coming home," Bourn said. "But then I thought, `Hey, it's baseball. Just go out and play.' That's the bottom line."

It was something he'd done all his life, but the transition to Houston did not go well at first. He struggled with injuries in his first year with the Astros, batting just .229 with a .288 on-base percentage, lowest in the Majors. But there were also 41 stolen bases, a tipoff on the kind of basepath threat he could be.

Last season, Bourn blossomed with a .285 batting average that included 27 doubles and 12 triples and those 61 steals, numbers that added up to being named the Astros' Most Valuable Player.

Now he's a fixture leading off for the Astros, using his speed to fuel rallies and score runs. And, oh yes, to steal bases.

Hal Bock is a freelance writer based in New York.