Ryan Braun tested positive for elevated levels of testosterone during the 2011 postseason. He took a second test at an independent laboratory, according to the New York Times, that showed normal levels of testosterone. The reason for the difference? Not known, and almost impossible to prove either way after the fact.
The reason that Braun avoided punishment? An improperly handed sample, according to the Times:
Under Major League Baseball’s Joint Drug Prevention and Treatment Program, the testing service, Comprehensive Drug Testing, Inc., "absent unusual circumstance" is supposed to send specimens to the testing laboratory in Montreal on the same day they are collected.
Braun’s lawyers argued that his sample was not sent for roughly 48 hours.
Some might describe the delay as a "technicality." Others might describe the delay as a "violation of protocol", which could be something that messes with the science needed to prove something beyond a reasonable doubt. I'm sure the people who have quickly decided which one it is will be willing to change their mind after more of the story is known.