A football match is being played. During a tussle on a set piece, Player 1, the home side's star striker, engages in a tussle with Player 2, the visitors' big summer signing. The pair grapple, Play 1 is stronger, and therefore Player 2 is flung to the ground with not-insignificant force. Normally, that's the end of it -- perhaps the referee has a chat with them both, perhaps cards are issued if there was previous misbehaviour, but mostly this would represent a non-incident.
But Diego Costa doesn't have 'non-incidents'.
Like Mario Balotelli at Liverpool, Costa's reputation proceeds him. There is a 'dark side' to his personality, we're told, and that dark side will be gleefully pointed out at every opportunity. Take, for instance, the time he was subject to a bad tackle in pre-season and got angry at the perpetrator -- 'Diego Costa could be the Premier League's new pantomime villain after Chelsea move', bleated the Mail. Take, for another instance, the bizarre yellow card he was shown at Burnley after being hacked down by Tom Heaton in the first half. And, for a third instance, why not re-live Roberto Martinez's atypically snide post-game presser from two weeks ago?
Diego Costa is being set up to be the bad guy, so it's not surprising that the Sigurdsson incident has been horrendously overblown. Fortunately, the FA didn't bite on the clash, but that hasn't stopped him being villified anyway. 'Man doesn't get suspended for thing he shouldn't have been suspended for' is a less sexy headline than 'Diego Costa escapes punishment for lashing out at Swansea's Gylfi Sigurdsson', I suppose.