The second-winningest coach in NBA history has decided to call it quits so he can spend more time with his family.

Dallas Mavericks head coach Don Nelson resigned Saturday and assistant coach Avery Johnson, who has coached several games this year and was being groomed to be Nelson's successor, takes over the team immediately.

"Mavericks owner Mark Cuban told ESPN.com that Nelson resigned Saturday "for family and other reasons."

"Nelson, the second-winningest coach in NBA history, has missed several games in recent weeks to be with his wife while she recovers from surgery."

Nelson also coached the Milwaukee Bucks, Golden State Warriors and New York Knicks.