FORT MYERS, FLA. - It's bad form for ballplayers to boo, even if they want to, so Darin Mastroianni never did. But he didn't have to -- millions of fans in stadiums around the country expressed his annoyance by hooting their own.

And in doing so, the Twins outfielder believes, they eventually delivered base-stealers like him a valuable gift.

"I know the rule was never popular with fans. You always hear the whole stadium boo whenever you see someone try it," Mastroianni said of baseball's least-effective -- but perhaps subtly more important than its critics realize -- pickoff play: the fake-to-third-throw-to-first jitterbug. "I should thank them."

That's because Major League Baseball, responding to critics outside the game and within, amended Rule 8.05(c) over the winter to redefine all fake pickoff moves, to any base, as a balk. Since the fake-and-whirl two-step was used only on first-and-third situations, and especially since so few runners are ever picked off by the outlawed play, most fans, and even plenty of ballplayers, believe the effect will be negligible.

But where fans may see relief, base-stealers such as Mastroianni and Jamey Carroll see opportunity. Most pitchers' goal in utilizing that deception, they point out, isn't to pick off the runner, though that's a nice benefit when it happens. The real reason for the fake is to freeze the runner at first.

And that's not legal anymore.

"It changes everything as a baserunner. It could be a big change," said Mastroianni, who stole 21 bases in 24 attempts last season, his first with the Twins. "When you're on first, you really have to be careful [against righthanded pitchers], because you can't be sure where he's going, if he's coming over to first. You have to hesitate."

Now, however, baserunners know the moment a pitcher's left foot rises that he is committed to throwing the ball, either to third base or the plate, giving them a better jump toward second.

"It's definitely going to change the aggressiveness of guys at first base," said Carroll, who has stolen 31 bases in 40 attempts over the past three seasons. "I don't know how it'll turn out, but I instantly feel I can be more aggressive. The possibility of a fake always made you pause a little bit."

Some managers go even further. "Watch the stolen bases jump this year," Orioles manager Buck Showalter predicted to FoxSports.com last week. "It shuts down the first-and-third. A righthanded pitcher had to have that move -- otherwise, you're giving up 90 feet all the time."

The Major League Baseball Players Association even blocked the rule change last year, with executive director Michael Weiner saying, "It's not a huge deal, but our guys would prefer it not be eliminated," according to the New York Times. But owners instituted it unilaterally for this season.

Twins pitchers mostly say they are not alarmed by the change, that it just puts a little more responsibility for holding runners on their shoulders.

"If you stay aware, if you vary your looks, vary your time to the plate, you can keep [the runner] close," said Mike Pelfrey, who said he had never picked off a runner with the move. "Throw over [to first] more, come to a stop, just change it up."

Cole De Vries, in fact, said he was on the side of the booing public.

"It's a ridiculous play. When you get to this level, maybe one out of 500 times, you might get a guy who's not paying attention," the second-year Twins starter said. "I'm glad it's not there anymore. I don't really foresee it having any bearing on the game."

Well, it won't occasionally embarrass a distracted runner. Mastroianni is glad for that.

"I can't tell you how many times I've been picked off by that. More than once," he admitted. "If a guy does it well, and you're looking to go, it gets you. But much more than that -- how many times have I not gone, when I know I could normally get there? It's going to give good baserunners a chance to get into scoring position more easily."