Former Microsoft CEO Steve Ballmer is now leaving his seat on the software company's board of directors, so he could spend more time on his new project, the LA Clippers.

Ballmer wrote to his successor Satya Nadella Tuesday to say that his commitments in retirement - including his US$2 billion acquisition of the LA Clippers - led him to decide to give up his board seat.

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The resignation is effectively immediately.

Ballmer gave way to Nadella as CEO in February, ending a run that began in 2000 when he took over from founding chairman Bill Gates. Ballmer also stressed in his letter that he currently stands as Microsoft's largest individual shareholder and doesn't see that changing in the near future.

The new Clippers owner owns more than 333 million shares of Microsoft worth over US$15 billion. Chairman Gates currently owns 298 million shares.

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

Ballmer also wrote about a hectic fall schedule, between the start of the NBA season, and some teaching that he plans to do, which prodded him to resign.

He stressed, however, that he remains committed to the company.

"I bleed Microsoft, have for 34 years and I always will," Ballmer wrote. "Count on me to keep ideas and inputs flowing. The company will move to higher heights. I will be proud, and I will benefit through my share ownership."

The day before his retirement, Ballmer joined Clippers fans at a rally with his famed all-out enthusiasm that people at Microsoft have seen often when he speaks at developer conferences.

"We're looking forward," Ballmer proclaimed at the Clippers rally at LA's Staples Center, taking off his blue Clippers hat. "Everything is about looking forward."

Ballmer's fervor at the rally was in stark contrast to disgraced former owner Donald Sterling, who never spoke to the media, and was famously - or infamously - frugal when it came to spending on the team during its long losing streaks, despite a vast fortune amassed through real estate. 

Forbes' lists Ballmer's worth at $21.9 billion in its ranking of the world's real-time billionaires.

TagsClippers, Steve Ballmer, Bill Gates, Satya Nadella