"The bottom line is, outside of an athlete removing his hands off the track or his feet leaving the blocks, nothing else is a false start," David Katz, one of 17 members on the rule-making IAAF technical committee, told Reuters by telephone.
The need for improved quality and consistency by starters worldwide had prompted the clarification, said Paul Hardy, IAAF competitions director.
Usain Bolt's false start at last year's world championships in Daegu, while a clear violation, only added to the discussion.
"This allows a safety valve," said international starter Tom McTaggart, who has been sending off athletes for more than 40 years.
"It takes a little pressure off the starter in general, the recall crew and the athletes. They (the athletes) know 'I got a second chance here'."
Spectators and starters might need to adjust, McTaggart told Reuters.
"Fans may say: 'that guy moved, so it's a false start'," the 1996 Olympics starter said. "It will be a little bit of a learning curve."
Starters might wind up disqualifying athletes less often, he noted.