Niasse's is a blatant dive, but the retrospective punishment system will be farcical if there's no consistency when reviewing the incident. As yhou'll probably recall, Carlisle's Shaun Miller was retrospectively banned, having been adjudged to have dived to win a penalty against Wycombe. If you watch the incident, he tried to get straight back up to play on and didn't claim a penalty, yet was found guilty nonetheless:
Link:
Shaun Miller "dive"
