False start: any swimmer leaving the block before the starting signal = disqualification (zero-tolerance, consistent with World Aquatics 2010-onward standard); Stroke violations: improper stroke mechanics per the rule book — DQ from the event; Turn violations: improper turn execution — DQ
Why people argue about this
People often argue that a false start is only penalized if it's caught by an official, thinking they can get away with it as long as no one sees them. Actually, the rule states you're disqualified for attempting to move before the starting signal, regardless of whether anyone notices or not.
