Marcelo is a pretty decent footballer, which you might have deduced due to the fact that he plays regularly for Real Madrid. Unfortunately, Marcelo is also a bit of a dirty player and a serious wind-up artist. It's rumored that the Madrid fullback has been the victim of racist abuse when playing against Barcelona in the past, but even something as disgusting as racism doesn't excuse this equally disgusting challenge by Marcelo on Cesc Fabregas. Of course, it incited a brawl
I'm no Cule, but I'm going to have to come to the defense of the Barcelona players who started the brawl in this situation. Marcelo made no attempt on the ball, and while it is dangerous to guess at the intent of players, it seems fairly clear that Marcelo's intention was either to intimidate or injure Fabregas. Nothing about that tackle was done to improve his team's chances of winning a football match, so the reaction of the Barcelona players was understandable.
What Marcelo did has absolutely no place in the game, and he will be lucky if the LFP does not hit him with a lengthy suspension in La Liga.