Warning: At these Olympics, sprinters will get no warnings.
Under the zero-tolerance false-start rule in place for the London Games, a sprinter's mistimed jump from the blocks could destroy four years of hard work in an instant. If that runner happens to be, say, Usain Bolt, it could turn one of the most anticipated moments of the entire Olympics into one huge downer.
Under the old rule, the entire field was given a warning after the first false start and the disqualifications began with the second one. Under the new rule, the first person to jump is out - no second chances.
The new rule goes on display on the sport's biggest stage Friday when the women line up for the 100-meter heats. Bolt, seeking back-to-back titles in the marquee race of the Olympics, hits the track Saturday.
''A double-edged sword,'' 2004 Olympic champion Justin Gatlin calls the new rule, which took effect in 2010. ''Because some people can take advantage of it if it's two or three false starts and no one is getting charged. At the same time, you can have something like last year with Bolt.''
Last year was track and field's worst nightmare.
In the 100-meter final at the world championships in Deagu, South Korea, Bolt burst from the block early. Gone. He ripped his shirt off and skulked off to the practice track. Fellow Jamaican Yohan Blake ended up winning the race, but the win carried with it a huge asterisk because the world-record holder was absent from the field.
''I've learned not to worry about the start anymore,'' said Bolt, who at 6-foot-5 has always had trouble with the start. ''I've sat down and talked with my coach and we have come up with the conclusion that, back in the day, I was never a good starter.''
But if Bolt is unworried, it hasn't played out that way on the track, where his starts through the spring and summer have ranged somewhere between cautious to lumbering to abysmal.
He clambered out of the blocks in all three of his 100-meter races at the Jamaican Olympic trials. Against most runners, he can make up the ground he loses with the slow starts, but not against Blake, who beat Bolt in both the 100 and the 200 that weekend in Kingston. Bolt later conceded he was less than 100 percent for that race. Either way, his trouble in the starting block has contributed to an equation shift at this year's Olympics, and the questions have persisted about any hangover Bolt - and the sport itself - might have endured from his DQ in Deagu.
''That's awful that our sport's biggest star wasn't in the final,'' said American sprinter Allyson Felix. ''We just can't have that. We're already a struggling sport and that's killing us. For that reason alone, it shouldn't be in play.''
Felix is among critics who wonder if officials from track's governing body were trying to solve a problem that never really existed.
The international track federation voted to adopt this dramatic shift in an attempt to speed up races and reduce gamesmanship. When the old rule was in effect, it wasn't uncommon for a slower starter to intentionally take the first false start in an attempt to slow down the rest of the field.
''What is gamesmanship?'' said Jon Drummond, the retired sprinter who now coaches Tyson Gay. ''They don't throw people out of the 10,000 because somebody pushed somebody's hip. It's called adrenaline. You have adrenaline rushing because they want the gun to fire. I think it's part of the sport. I think it's part of the drama. It's a good thing to talk about. But hopefully we'll get back to'' the old rule.
Anyone who's been following track for a while knows Drummond is the all-time champion when it comes to protesting a false start.
The year was 2003, and at world championships, track and field was debuting the one-warning-for-the-field rule that went by the books with the newest incarnation. Before that rule, everyone in the field was allowed a warning, which often delayed starts by several minutes.
Much of the track world didn't take an early liking to the rule, and it didn't get any more popular when five runners were disqualified from the 100.
Nobody took umbrage more than Drummond, who fell to his back in the middle of the track, cradled his head in his hands for nearly 15 minutes and said, ''I didn't move, I didn't move,'' while race officials tried to move him off the oval. Eventually, they did, but he used that opportunity to roll around on the grass and jump in the water in the steeplechase pit. Eventually, the IAAF suspended him for the rest of the season for conduct deemed ''unsportsmanlike and likely to bring the sport into disrepute.''
Now that the false-start rule has been made even more stringent - and now that the sport has seen its biggest star removed from a big race - the IAAF has responded by inserting a clarification into the rulebook.
Written in March, it states that if a runner flinches but his foot does not leave the starting block, he can be warned but not charged for a false start. What that really does is give the starter more discretion before automatically booting a runner from a race.
''It's a question of interpretation,'' said Nick Davies, a spokesman for the IAAF. ''There has been no rule change.''
Last month in Jamaica, 2008 100-meter silver medalist Kerron Stewart saw just how friendly the interpretations could be. The false-start gun went off and a video replay showed Stewart moving before everyone else, but race officials put her back in the race. Stewart ended up qualfiying and is considered one of the favorites in London.
''I'm not sure what happened,'' she said. ''They said it was something with the starter but I'm not sure. I know I didn't flinch. I know I heard something, so I know I didn't break. I was never worried.''
To hear some of track's greats tell it, though, maybe the sport should rethink its strategy.
''The best rule was the one before this one,'' said four-time gold medalist Michael Johnson. ''This one now is not realistic and that was evidenced last year with Bolt. He false starts and fans are robbed of seeing him run. Bottom line, you can't have people false starting. There's some responsibility on the IAAF there. There's also some responsibility on the athletes to be professionals and stay in the blocks.''
AP Sports Writers Pat Graham and Raf Casert in London contributed to this report.