Well this is something of a stunner, just a week after Chicago Cubs President Theo Epstein said all of the coaching staff would be back next year, with the exception of assistant hitting coach Mike Brumley.

Here are the reports on hitting coach Bill Mueller resigning:

Sources: Bill Mueller has resigned as Cubs hitting coach. — Patrick Mooney (@CSNMooney) October 7, 2014

Breaking Cubs news. Source: Cubs hitting coach Bill Mueller has resigned. Story coming on http://t.co/lNa8FQCEpg — Jesse Rogers (@ESPNChiCubs) October 7, 2014

I’m sure we’ll soon learn more on the reason for the change, whether it was driven by the Cubs or by Mueller, but, for now, it’s just a surprise. The Cubs have had so much turnover in the hitting instructional group over the last three years, and now they’ll have to revamp once again. There are strong rumors that Manny Ramirez could join the coaching staff, and now it’s not just the assistant hitting coach gig that’s available, it’s the main hitting coach gig, too.

It’s possible that the Cubs could go out and get an established big league coach/hitting guru to be their new hitting coach, with Ramirez sliding in as the assistant hitting coach. In fact, right now, that’s what I’d guess we’re going to see.

Until then, I hope we find out what exactly happened with Mueller, whom the front office seemed very enthused about just one year ago.

UPDATE: Indeed, Mooney reports that the Cubs will focus on finding an established hitting coach, rather than a first year coach, for the main hitting coach job.

UPDATE 2: It sounds like Brumley leaving was the tipping point for Mueller:

Story to be posted momentarily but told Mueller was torn in taking the job in the first place and he was "comfortable" with asst Brumley.. — Jesse Rogers (@ESPNChiCubs) October 7, 2014

Brumley was dismissed after the season..apparently made Mueller's decision easier…Cubs did want Mueller back — Jesse Rogers (@ESPNChiCubs) October 7, 2014

That’s something of a bummer.