The derailleur could lock up and cause the rider to lose control of the bike, according to the official announcement. Rear derailleurs from the SRAM Red 10-speed medium groupset with serial numbers 31T2000000 to 11T39999999 are affected. The rear derailleurs were offered in stores between September 2012 and November 2013. They were also fitted to complete bikes.
End users should contact their bike dealer. The rear derailleur will be replaced free of charge.