Chris Davis' breakout really started in 2012, when he finally played a significant portion of time for the Orioles and had a wRC+ of 121. He hit a scorching hot .320/.397/.660 in the Sept/Oct monthly split in 2012 and simply continued to hit baseballs really hard in 2013. Davis crushed opposing pitchers in 2013, yet he fell back down to earth and crashed in 2014. Davis, for reference's sake, is a lefty pull power hitter.
J.D. Martinez had a breakout year last year after being picked up by the Tigers from the Astros. Martinez made adjustments in his swing, and off he went for a 153 wRC+ in 480 PA. Martinez has not yet fallen back down to earth despite a low walk rate and high strikeout rate. For reference's sake, Martinez is a righty pull power hitter.
Recognize that Davis and Martinez have very similar batted ball profiles (at least in 2015). Naturally, fly balls are the focus.
All the following data are from FanGraphs.
For pull power hitters, they sure don't pop up much. That's not necessarily relevant to this article, but I thought it was interesting nonetheless.
Davis and Martinez both have a similar difference between their walk rates and strikeouts rates. Davis walks more and strikes out more (Martinez walks less and strikes out less, of course), but the difference between each player's rates is about 20 percentage points. The point is that these hitters are very similar, but there is a not-so-subtle difference between Martinez and Davis - J.D. pulls the ball a lot less.
To show that point, I've calculated pull ratios for each player/batted ball type combination by dividing the pull percentage by the opposite percentage (career values). Chris Davis outstrips Martinez in each batted ball type.
The largest differences in terms of percentage is line drives, the fly balls, then ground balls. Surprisingly, in terms of pull ratios, J.D. Martinez and Chris Davis are the most similar on ground balls. I'll take this moment to remind you that those numbers above are career values. In 2015, J.D. Martinez's pull ratio on ground balls is at 13.2, slightly higher than Davis', much higher than his own career value, and definitely worthy of shifting. Yet, each player's production on ground balls is very different due to the effects of the shift.
Chris Davis is one of the most shifted on players in baseball. Sure. Obvious. However, since detailed, granular, shifted-on information is not publicly available, I turned to the fine folks at Bless You Boys for some insight on J.D. Martinez against the shift. Basically, none of the writers there have seen much shifting against Martinez. Against the Tigers, opposing teams shift the most against Victor Martinez, Alex Avila, and sometimes Miguel Cabrera.
This is somewhat strange; J.D. Martinez, with a 5.64 pull ratio on ground balls for his career and a 13.2 pull ratio this year, is probably shiftable. Maybe there's not enough data available to make an informed decision on whether or not to shift on Martinez, but the difference in shifting appears when comparing the two players' production on ground balls over time.
PRD calculated by 1.7*BA+SLG. A quick-and-dirty OPS-like measure that weights getting on base more appropriately.
That's a massive difference in production, especially in 2014 and 2015. One possible explanation for the difference in production aside from the pull ratios/shifting angle is that Martinez might just be hitting ground balls harder than Davis is. That's not necessarily the case.
Martinez, in terms of soft-hit rate on ground balls, has either been very close to Davis or hit way more soft grounders. That doesn't take into account the distribution among medium and hard-hit balls, though. Martinez, in general, has more soft-hit and hard-hit grounders than Davis does. Davis has many more medium-hit ground balls. It's not entirely clear how those distributions relate to batted ball production, but I'm willing to concede the possibility of an effect outside the shift.
The differences in production do not manifest themselves on balls in the air. By fly balls and line drives, Martinez and Davis don't have the differences in production that appear with ground balls.
Overall, J.D. Martinez is currently pulling the ball on the ground just as much as Chris Davis is, yet his ground ball production is far higher perhaps due to the lack of a shift against him. Davis, to his credit, is still hitting the ball in the air so hard that he has an above average wRC+ this year (117), so he's not completely ruined (he's also had other issues with medications that could be involved).
Since there are few differences elsewhere in their profiles, the difference in total production at the plate can almost entirely be attributed to the differences in ground ball production, for which the shift is a significant factor. Davis is being severely hurt by the shift; Martinez is barely seeing the shift. Eventually, if Martinez keeps pulling the ball like he is now, he'll start seeing three guys to the left of second base. It's up to him if it will ruin him.
. . .