Edwin Jackson's slider was much more effective with the White Sox than Diamondbacks. Did it have anything to do with command? (AP photo)
Within a week of being dealt to the White Sox, Jackson had already credited Don Cooper with improving his mechanics. That tweak likely is why Jackson was significantly more effective with the White Sox than Diamondbacks, as he threw harder across the board and saw his strikeout-to-walk ratio skyrocket.
But Jackson's slider saw the most improvement. He threw it about one in every four pitches with Arizona at an average of 85.4 miles per hour, and it was a few ticks above average at 0.56 w/RC. With the White Sox, Jackson threw his slider 36.1 percent of the time at an average of 87.6 miles per hour—and, not surprisingly, the pitch was worth 2.28 runs above average per 100 pitches.
Before researching this, I figured Jackson's slider was more effective with the White Sox because of better command—remember, Gavin Floyd's curveball and John Danks' changeup have been at their most effective with great command. Better command helped, but the increased velocity similarly was beneficial:
Images via Texas Leaguers' pitch f/x database
Jackson's command was better with the White Sox, but it wasn't as significant of an improvement as his increase in velocity. He still generally threw the slider low in the strike zone or low and out of the strike zone with both teams.
On 477 sliders thrown with Arizona, 64.2 percent were for strikes with 51.2 percent being swung at. With the White Sox, Jackson threw 302 sliders with 68.2 percent going for strikes and 56.6 being swung at. But opponents' whiff rates stayed the same between Jackson's two stops, with about one in every five sliders resulting in a swing and miss with both teams. With improved command and velocity, though, Jackson's slider was much more effective by inducing worse contact.
What's interesting is the swing percentages. Usually, we'd figure that increase would be due to a lack of familiarity that comes with switching leagues and divisions, but Jackson pitched all of 2009 in the AL Central and was with Tampa Bay for three years before his stop in the Motor City. The American League knew Edwin Jackson much better than the National League.
But Jackson returned to the American League as a new pitcher, and Jackson's opponents certainly hadn't seen him throw as well as he did with the White Sox. They'll be able to adjust better to him in 2011, and it's up to Jackson to find a way to counter that.
Speaking of opponents, the crew at South Side Sox would probably want me to point this out: the quality of the teams Jackson faced wasn't exactly top-notch, at least on the surface. But digging into the numbers, Jackson actually faced some fairly quality lineups:
- Boston (1): .345 wOBA, 2nd in baseball
- Detroit (4): .329 wOBA, 10th in baseball
- Kansas City (1): .322 wOBA, 15th in baseball
- Oakland (1): .315 wOBA, 20th in baseball
- Cleveland (2): .312 wOBA, 22nd in baseball
- Baltimore (2): .309 wOBA, 23rd in baseball
Five of Jackson's 11 starts came against offenses in the bottom half of baseball and five came against offenses in the top half, with Kansas City right in the middle. Granted, all three of Jackson's starts with the Sox in which he allowed four or more earned runs came against Detroit or Kansas City (he also allowed four runs—three earned—against Boston), so Jim & Co. still do have a point.
Despite all that, I'm still confident Jackson will put together a fine season in 2011. He made real improvements with the White Sox, and a lot of those were with his slider.