After trading Denard Span to the Nationals earlier in the off season, it seemed rather odd that the Minnesota Twins would also trade his replacement, Ben Revere. However, the Twins improved their present rotation with Vance Worley in the deal and also received a decent prospect in Trevor May. With the myriad of problems the Twins had last season, the pitching was the largest problem and Worley should be a nice improvement.
To be honest, Revere for Worley straight up would have been a good deal for the Twins. To get May in the deal as well is a bonus. You might not agree from casually looking at Worley's statistics for 2012. A 6-9 record with a 4.20 ERA and 1.511 WHIP hardly seems like an improvement for the Twins who gave up more hits as a pitching staff in 2012 than any other American League team. The Twins also finished next to last in runs allowed and homers allowed and were dead last in strikeouts.
But sometimes you have to go deeper than those surface stats to see the bigger picture. The linked article at the top of this post indicated that Worley battled most of the year with a bone chip in his elbow. The chip was removed in a September operation that ended Worley's season. If you look closely at Worley's numbers, you can see the effect of the injury in his pitching.
For example, His velocity was down slightly and his slider went from being a very good pitch for him in 2011 to being terrible in 2012. His fastball also went from 10.2 runs above average in 2011 (7.3 according to PitchF/X) to -0.6 in 2012 (-3.1 for PitchF/X). Clearly, the elbow problem had to figure into some of the loss of effectiveness in those pitches.
The clearest indicator of the problem came with how he fared against left-handed batters. In 2011, he held left-handed batters to a triple slash line of: .201/.271/.299. Those numbers went silly in 2012 and against those same sided batters, his triple slash line was: .312/.386/.462.
One last indicator of how the injury affected his pitching: In 2012, batters across the board had better plate discipline against Worley last season. During his cup of coffee season in 2010 and his larger season of 2011, batters would swing at 28 percent of Worley's pitches out of the strike zone. That number fell off to 26.4 percent in 2012. It seems pretty clear that Worley was not as able to fool batters last year as he did the year before.
Even so, Worley's season was not quite as bad as it looked. His ERA was 4.20 but his FIP was 3.85. His xFIP and SIERA were also lower than his actual ERA. Some luck had to be involved too as his BABIP rose to an extremely high .340 after finishing at .283 the season before. Also consider that in all nine of Worley's losses, the Phillies scored two runs or less.
What should we expect from Vance Worley in 2013? His strikeout rate should remain nearly the same. His 7.2 rate per nine in that category was almost a full strikeout less than his 2011 rate. But that will be offset from not pitching to pitchers every nine at bats. His three-plus walks per nine should improve as the Twins really emphasize that aspect. His OPS against at home last year was a ghastly .861 compared to .739 on the road. With friendlier dimensions at Target Field, those numbers should improve.
The key for the Twins will be how well Worley bounces back after his surgery. If his pitches return to the bite of 2011, then they will have made one heck of a deal. But even if he pitches to his 2012 numbers, which seems hardly likely, he will be better than three of the five rotations spots the Twins were throwing out there last season.