It was actually pretty hard to pick which Boston Red Sox hitter to highlight here. Their team wRC+ of 85 in the second half was tied for the second-worst mark in baseball, and there were actually three Boston players among the 30 worst hitters following the All-Star break when looking at wRC+.
But instead of going with Xander Bogaerts or Hanley Ramirez, we went with the one who struggled the most in this metric, Jackie Bradley.
After enjoying a breakout year in 2016, Bradley took a step back at the plate in 2017 -- his wRC+ went from 119 to 90 and his fWAR was slashed significantly (5.0 to 2.3) because his Offensive Runs Above Average rating went from 20.0 to -1.8.
If we just looked at his performance in the first half, though, he was on track to post even better numbers than he did in his breakout campaign. His wRC+ (122) and OPS (.853) were slightly better, while his .210 ISO wasn't much different. But then the bottom dropped out following the midsummer classic, and he just couldn't get anything going.
Bradley's wRC+ (51), OPS (.579), and ISO (.098) in the second half made him look like a shell of the hitter he was, and his contact numbers deteriorated. The below table shows his contact outside the strike zone (O-Contact%) and inside the strike zone (Z-Contact%) from the first half to the second half, along with his ground-ball rate (GB%), fly-ball rate (FB%), and hard-hit rate (Hard%).
| 2017 | O-Contact% | Z-Contact% | GB% | FB% | Hard% |
|---|---|---|---|---|---|
| First Half | 60.2% | 81.5% | 44.7% | 35.7% | 37.5% |
| Second Half | 61.3% | 75.6% | 54.4% | 28.8% | 28.1% |
Upon seeing numbers like these, it shouldn't be surprising that Bradley's power disappeared -- it's hard to consistently hit balls with authority when the ones you're swinging at aren't in the strike zone.