There is a lot of fairly boring back-and-forth debate over hedge fund activism, in which proponents of activism argue that it's good because it improves corporate performance, and opponents of activism argue that it's bad because it provides only short-term boosts but is destructive in the long run. There are studies both ways, each side picks the evidence it likes, and it remains an eternally suspended question that in any case tells you nothing about whether any particular activist proposal is good or bad. We examine the product market spillover effects of hedge fund activism (HFA) on the industry rivals of target firms. HFA has negative real and stockholder wealth effects...