Apparently, the NFL agreed with the coach.
Brown was fined $10,000 by the NFL for unsportsmanlike conduct, according to the Pittsburgh Tribune-Review.
The incident occurred with the Steelers up 27-9 in the third quarter, when Brown fielded Sav Rocca's punt at his own 22. Breaking through a wave of Redskins defenders, Brown took off for the end zone. Nobody came close, prompting him to spin around at the Washington 20 and backpedal in to the endzone.
Ultimately, the play was called back because of a block in the back.
This makes the third unsportsmanlike conduct penalty for Brown, dating to last year's preseason.