Haydn’s “bloody harmonious war” is the composer’s punning description of the rivalry in London between the concert organization for which he worked, headed by the violinist Salomon, and the ‘Professional Concert’, whose star attraction in 1792 was Haydn’s former pupil, the composer Pleyel. Haydn’s vocabulary, mixing metaphors musical and combative, reflects how newspapers projected this phony war. Pleyel was linked to Wilson Braddyll, England’s leading advocate for pugilism. One report even suggested that only by resorting to the law might the conflict be resolved. Haydn and Pleyel really did find themselves in court, called as deponents in a lawsuit between their publishers begun in 1788. Although interpretation of this case has hitherto focussed on Haydn’s supposed misappropriation of compositions by Pleyel, evidence presented here for the first time shows that the latter was equally culpable, having made unauthorized use of several compositions by his erstwhile teacher. The root of the case, however, lay in establishing ownership of publication and other rights, which Haydn effectively always turned to his personal advantage to the perceived detriment of others. As a souvenir marking the end of the whole episode, the triumphant reception of his compositions in the 1792 season, Haydn acquired a print for his collection, its subject referencing the “war’s” principal themes and personalities.