It's a complicated story, so read the whole thing at "Sharon Osbourne Is Out at 'The Talk'" (Hollywood Reporter). I'll just excerpt some highlights, which I don't expect you to understand if you don't know the context.
From the statement by CBS: "As part of our review, we concluded that Sharon’s behavior toward her co-hosts during the March 10 episode did not align with our values for a respectful workplace."
From Hollywood Reporter: "The news came two weeks after the March 10 dustup, one that was followed by multiple allegations of racist comments from Osbourne being levied by former co-stars Leah Remini and Holly Robinson Peete.... After Robinson Peete... alleg[ed] Osbourne had referred to her as 'too ghetto,' Remini... claimed that Osbourne had made racist comments about former colleague (and Chinese American woman) Julie Chen, homophobic remarks about The Talk creator and then-moderator Sara Gilbert and made anti-Italian slurs toward Remini herself.... [Osbourne] gave interviews to both Variety and Entertainment Tonight, claiming that she had been 'set up' by the producers and was offered up as a 'sacrificial lamb.' Her publicist also issued a doozy of a statement, alluding to Remini and Robinson Peete's comments by noting 'The only thing worse than a disgruntled former employee is a disgruntled former talk show host.'"
Now, Osbourne is the "disgruntled former talk show host." So we'll see what else she has to say.