This is what the cast list of the IMDB page for "Castle" looks like:
What’s wrong with this picture? Hmmm, what’s the show about? A mystery writer (Rick Castle played by Nathan Fillion, top billing) who follows a detective around, basing his new book character on her. That’s Kate Beckett (played by Stana Katic). She shares what I reckon would be pretty much equal screen time with Fillion, maybe a bit less, as Fillion has a fair bit of time on screen with his family, mother Martha and daughter Alexis. But pretty much equal. In the credits, Katic is second billed. So why, on the IMDB page, does Katic come in fourth in the cast listing? Behind her two sidekick detectives, who do both get reasonable screen time, but certainly aren’t the focus of the show as Beckett and Castle are.
Is there a legitimate reason for this cast order? Not alphabetised, so, why does the female lead come in behind two lesser characters?