An excellent author on US Competition Law is Richard Posner, a federal judge in Chicago and one of the great intellectuals on the bench. He had a blog (together with an economist) at http://www.becker-posner-blog.com/ (sadly discontinued after his co-author's death in 2014).

Posner has literally written the book on the US' Antitrust law, and he is one of the rare writers I enjoy reading even when I vehemently disagree (as I do with his proposal for a largely unregulated market in babies).