"Crash" Davis (Costner), a veteran of 12 years in minor league baseball, is sent down to the single-A Durham Bulls for a specific purpose: to educate hotshot rookie pitcher Ebby Calvin LaLoosh (Robbins, playing a character loosely based on Steve Dalkowski) about becoming a major-league talent, and to control Ebby's haphazard pitching. Crash immediately begins calling Ebby by the degrading nickname of "Meat", and they get off to a rocky start.
Thrown into the mix is Annie (Sarandon), a "baseball groupie" and lifelong spiritual seeker who has latched onto the "Church of Baseball" and has, every year, chosen one player on the Bulls to be her lover and student. Annie flirts with both Crash and Ebby and invites them to her house, but Crash walks out, saying he's too much a veteran to "try out" for anything. Before he leaves, Crash further sparks Annie's interest with a memorable speech listing the things he "believes in", ending with "I believe in long, slow, deep, soft, wet kisses that last three days... Good night".
Despite some animosity between them, Annie and Crash work, in their own ways, to shape Ebby into a big-league pitcher. Annie plays mild bondage games, reads poetry to him, and gets him to think in different ways (and gives him the nickname "Nuke"). Crash forces Nuke to learn "not to think" by letting the catcher make the pitching calls (memorably at two points telling the batters what pitch is coming after Nuke rejects his calls), and lectures him about the pressure of facing major league hitters who can hit his "heat" (fastballs). Crash also talks about the pleasure of life in "The Show" (Major League Baseball), which he briefly lived for "the 21 greatest days of my life" and to which he has tried for years to return.
Meanwhile, as Nuke matures, the relationship between Annie and Crash grows, until it becomes obvious that the two of them are a more appropriate match, except for the fact that Annie and Nuke are currently a couple.
After a rough start, Nuke becomes a dominant pitcher by mid-season. By the end of the movie, Nuke is called up to the majors. This incites jealous anger in Crash, who is frustrated by Nuke's failure to recognize all the talent he was blessed with. Nuke leaves for the big leagues, Annie ends their relationship, and Crash overcomes his jealousy to leave Nuke with some final words of advice. The Bulls, now having no use for his mentor, release Crash.
Crash then presents himself at Annie's house and the two consummate their attraction with a weekend-long lovemaking session. Crash then leaves Annie's house to seek a further minor-league position.
Crash joins another team, the Asheville Tourists, and breaks the minor-league record for career home runs. We see Nuke one last time, being interviewed by the press as a major leaguer, reciting the clichĂŠd answers that Crash had taught him earlier. Crash then retires as a player and returns to Durham, where Annie tells him she's ready to give up her annual affairs with "boys". Crash tells her that he is thinking about becoming a manager for a minor-league team in Visalia. The film ends with Annie and Crash dancing in Annie's candle-lit living room.

Question: Why do the Bulls release Crash?
Answer: The Bulls do not need him anymore once Ebby is called up to the major leagues
Alternative answer: They have no use for Eddy's mentor