Nick Collison Announces Retirement By Luke Adams on May 10, 2018 in OKC Thunder Veteran big man Nick Collison is calling it a career, he announced today in an ESPN.com piece co-written by Royce Young. “I started in cold gyms in small towns in Iowa and ended up playing in more than 1,000 games over 15 years in the best league in the world. I’ve had an incredible run. I’m proud of my career,” Collison says in the article. “But it’s time to go.