A Ph.D. candidate researching battle rap soon becomes an obsessed competitor himself, hurling rhymed, politically incorrect insults at a variety of opponents. The free-wheeling, provocative third feature by veteran music video director Joseph Kahn is “a feverishly entertaining spectacle” (Variety) that was produced by Eminem and won the People’s Choice award in the “Midnight Madness” section of the 2017 Toronto Film Festival. DCP. 120 min.