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wOBA is just a Runs Created stat put onto a batting-average type scale. It uses total bases, unintentional walks with HBP, though it does add in bases per error. Which isn't going to affect anything here.
Would be weird for Fangraphs to take a 2014-15 luck stat and "average" it over the period 2012-16, but that may be what they did. If so I wouldn't put any special weight on Hammel's second halfs...