Former Microsoft CEO has stepped down from the company's board of directors. The move, which comes just six months after he retired from Microsoft, effectively severs Mr. Ballmer's ties to the company, though he is of course still its biggest individual shareholder. The question is: Why?

Ballmer, of course, recently purchased the Los Angeles Clippers NBA team for a record $2 billion. Not surprisingly, that is part of the reason.

"Given the multitude of new commitments I am taking on now, I think it would be impractical for me to continue to serve on the board, and it is best for me to move off," Mr. Ballmer writes in an open letter to Microsoft CEO Satya Nadella. "The fall will be hectic between teaching a new class and the start of the NBA season so my departure from the board is effective immediately."

Ballmer's letter describes how busy he's become since he left Microsoft six months ago. But he will not be giving up his Microsoft stock, a move that would effectively end his formal relationship with the company.

"I hold more Microsoft shares than anyone other than index funds and love the mix of profits, investments and dividends returned in our stock," he writes. "I expect to continue holding that position for the foreseeable future."

Microsoft CEO Satya Nadella also issued a public response to Mr. Ballmer's letter.

"While your insights and leadership will be greatly missed as part of the board, I understand and support your decision," Mr. Nadella writes. "As you embark on your new journey, I am sure that you will bring the same boldness, passion and impact to your new endeavors that you brought to Microsoft, and we wish you incredible success. I also look forward to partnering with you as a shareholder. On behalf of all of Microsoft and the Board of Directors, thank you."

And that's that.

After so many years at the company, so many years running the company, "bleeding Microsoft," as he says, Steve Ballmer is now just a Microsoft shareholder.