Bobby Jenks was the closer for the White Sox since late in their 2005 World Series championship season through 2009 -- and on and off last season -- though it wasn't an entirely smooth ride. Once able to hit 100 mph on the radar gun regularly, Jenks' average fastball velocity dipped into the low 90s in 2007 and 2008 before rebounding back to 95 mph in 2010. He also clashed with skipper Ozzie Guillen on multiple occasions, though Jenks always managed to keep his closer role.
Matt Thornton was even more dominant than Jenks the past few seasons. An under-the-radar pickup from Seattle before the 2006 season, Thornton worked with pitching coach Don Cooper and improved his control substantially after his initial time in Chicago. When general manager Kenny Williams declined to re-sign Jenks last offseason, the GM felt confident that lefty Thornton was ready to assume the closer role after striking out 81 batters in just 60 2/3 innings as the setup man last year.
However, the transition did not go as well as anticipated. Thornton blew his first four save opportunities in 2011, and Guillen was forced to pull the lefty from his new role by the end of April. While the White Sox's poor defense was partly to blame, Thornton's underlying rates weren't encouraging, either. He was walking more batters and striking out fewer, a dangerous sign for a pitcher.
Did Thornton simply not have the mental strength to handle the intensity of the closer's role?