Why did Robin Ventura challenge Nolan Ryan to one of the most memorable brawls in history?

Over the course of his 27-year career, Nolan Ryan won 324 games and struck out an all-time best 5,714 batters. It was presumably those feats of longevity and performance that made him a first-ballot Hall of Famer and placed him on a short list of the greatest pitchers of all time. Ryan is also remembered, however, for being involved in one of the most memorable brawls in baseball history -- and being someone you absolutely do not want to mess with.
On Aug. 4, 1993 -- the final season of Ryan's career -- the righty toed the rubber for a start against the White Sox. After Chicago third baseman Robin Ventura hit an RBI single in the first inning on a fastball over the plate, the 46-year-old Ryan was determined to not give him something that good to hit again. So, when Ventura came around again in the third inning, Ryan worked inside and ended up hitting him in the shoulder.
After taking a couple steps toward first base, Ventura decided to charge the mound. Almost immediately, it was quite apparent that he would regret that decision:

But like most on-field altercations, this beef didn't begin with the pitch that hit Ventura seconds before he charged the mound. 
Back in Spring Training before the 1990 season, White Sox utility infielder Craig Grebeck hit a home run against the Rangers -- and, according to who you ask, may have admired it a bit more than the opposition appreciated. Later that season, Grebeck hit his first career home run ... against Ryan, who again accused him of showboating. The very next week, Ryan plunked Grebeck, setting in motion a beanball war that gradually escalated to Ventura charging the mound and ending up in this headlock:

Ventura was ejected from the game for charging the mound, and -- as fate would poetically have it -- Grebeck was brought in to run in his stead. Ryan remained in the game and, on the very next pitch he threw, catcher Ivan Rodriguez picked Grebeck off first base.
According to future White Sox legend Paul Konerko -- who was in attendance that night -- the brawl created an electric atmosphere at Arlington Stadium that lasted the remainder of the game. "And I remember for every inning after that, the whole place was chanting 'Nolan' for what seemed like an hour long," Konerko said.
Maybe it was that energy that helped the Rangers come back from a 2-0 deficit at the time of the brawl to win the game, 5-2.
Though the Rangers and White Sox played another three-game series in September, Texas shuffled their rotation so that Ryan would not pitch in it. After what happened in August, that decision certainly made a lot of sense. Ventura would be the last -- and most memorable -- batter Ryan plunked in his career.