Mark Buehrle last pitched in 2015, for the Toronto Blue Jays. He was still pretty effective and toyed with the idea of pitching last season, but he never signed anywhere and is, for all intents and purposes, retired.
Now at least his number will be retired officially. It will be done by the club for which he had the most success and with which he is, obviously, most associated:
Buehrle pitched for the White Sox for 12 years. He was the model of consistency and durability in Chicago, logging over 200 innings a season in every single season but his rookie year, when he was primarily a reliever. He was a solid defender, a multi-time All-Star, tossed a perfect game in 2009 and helped the Chisox to their first World Series title in 88 years in 2005.
He was also one of baseball’s fastest workers, so I’m going to assume that, in his honor, the number retirement ceremony will last, like, a minute 20, after which everyone can get on with their dang day.