It's not often that a team cuts ties with an established closer before he accrues enough service time to qualify for free agency, but that's exactly what could happen with the White Sox and Bobby Jenks this winter. With a $7.5MM salary in 2010 and another year of arbitration eligibility left, Jenks' salary is only going to go up next season, possibility into the eight-figures.
Of course, the White Sox probably wouldn't entertain the idea of non-tendering their World Championship closer if his performance was in line with his compensation. His 4.44 ERA, .267 batting average against, and 3.08 BB/9 this season are career worsts, and it doesn't appear to be a one-year fluke either. Those three stats have gotten worse and worse every year since 2007, and Jenks will begin next season at 30-years-old. It's entirely possible that he's already reached his prime and is now on the way down.
Despite that, Jenks is still one of the better relief pitchers in the game. His 10.42 K/9 ranks right up there with other elite bullpeners, and after a gradual decline his average fastball velocity jumped back up to 95.0 mph this season. Jenks has also been victimized by some poor luck, with a .368 batting average on balls in play (league average is .302) and a 65.4 left-on-base percentage (72.0% league average). If those regress back to his career marks (.306 and 73.5% respectively), his ERA will almost certainly drop back down into the 3.00's.
The White Sox have absorbed a ton of salary obligation in the last two seasons, most notably in the form of Jake Peavy's and Alex Rios' long-terms deals, so they may decide that the money that would be spent on Jenks could be better used elsewhere. For what it's worth, the ChiSox already have a replacement closer in-house with Matt Thornton, and young (and cheap) hard-throwing setup men Sergio Santos and Chris Sale give the club some more options if nothing else.