Valdez had a couple of really good years with the Dodgers. He won 16 games in 1996, and won at least 10 games in four straight season from 1995 to 1998. Then, Valdez hit a wall and was traded to the Cubs before the 2000 season. His time in Chicago didn't last long, though. Half way through the year he was traded back to LA just in time to show his teeth against his former club. I'll let Wikipedia tell the story.
On August 27, 2000, Valdes was pitching for the Dodgers and was ejected from a game after he was accused of retaliating and throwing pitches at the head of Cubs first baseman (and Valdes' former teammate) Mark Grace. The incident began in the top of the fifth inning when Cubs pitcher Kerry Wood yielded the second of two home runs to the Dodgers' Bruce Aven. Wood then threw a pitch close to the next batter, Alex Cora, on the first pitch after Aven's second home run. Wood denied that he was trying to hit Cora, but in the bottom of the fifth, Valdes came close to hitting Grace on the first pitch, drawing a warning from home plate umpire Mark Wegner. Then, four pitches later, Valdes hit Grace on the shoulder, and was ejected. In September 2000, Frank Robinson, major league baseball's head of on-field discipline, suspended Valdes for six games and fined him $1,000 for the incident. Valdes initially appealed, but several days later dropped his appeal and began serving his suspension.I don't remember him being a tough pitcher. In fact, I always thought he was kind of meek. Anyway, I guess Valdez wanted to break that perception. Of course, maybe it was a bit of roid-rage. Years later he was named in the Mitchell report as a recipient of HGH.