According to a report in the German newspaper
The fight took place on March 27 at the Joe Louis Arena in Detroit, Michigan. Sauerland filed a protest with the WBC. The disqualified call was issued in the eleventh round when Dirrell slipped to the mat and Abraham hit him while still down.
One of the main points of the protest include referee Laurence Cole failing to call a knockdown in the tenth round. Abraham had knocked down Dirrell down with a hard hook but the ref waved it off as a slip.
Another point had to do with Cole not taking away any points or issuing warnings to Dirrell for throwing low blows.
The final point protests Cole's failure to call a break or being in position to break the fighters apart when Dirrell slipped, which allowed, in their opinion, the DQ punch to happen.