Plenty of footballers get insulted by the crowd, but they don't react because they are fully focused on the match.
Melo on the other hand plays with his head somewhere else, evidenced by his constant mistakes (the exact same mistakes he has been making all season) and his ridiculous antics on the pitch (dangerous elbows, laughing in the ref's face, arguing with fans)
What you call balls I call poor discipline. For some1 who makes €2.6m a year, I expect him to act like a professional footballer and not a loose cannon.