According to Snopes:
In 1974, feeling that his teammates had lost their aggressiveness and were too easily intimidated, (Dock) Ellis decided to put on a show against the Cincinnati Reds (who had come from behind to defeat the Pirates for the 1972 National League pennant on a run-scoring wild pitch in the bottom of the ninth inning of the final playoff game). In a May 1 start against the Reds — having announced before the game that "We gonna get down. We gonna do the do. I’m going to hit these motherfuckers." — Ellis opened the contest by drilling leadoff hitter Pete Rose in the ribs; hitting the next batter, Joe Morgan, in the side; and then plunking Dan Driessen in the back to load the bases. Although clean-up hitter Tony Perez managed to dodge Ellis' pitches long enough to draw a walk before being hit, Dock aimed his next two offerings at Cincinnati catcher Johnny Bench's head, whereupon he was unceremoniously yanked from the game by Pittsburgh manager Danny Murtaugh.