Who improved at the plate in the second half of 2015?
We usually turn to the tried and true method of analyzing players season by season. There's a point at which we have to demarcate sections of a player's career, and the beginning and end of a season give us a handy and obvious way of doing so. But there are often many changes and adjustments that go on within a season, and looking at six months of baseball as one unit misses a lot of trends that we might otherwise notice. With that in mind, today we're going to look at a few players who improved their eye and contact rate at the plate from the first half of the 2015 season to the second, giving consideration to how those improvements might help them in the upcoming 2016 season.
We'll be looking at the most-improved players for two main plate discipline statistics: the rate of swings at pitches outside of the strike zone, and the rate of contact on pitches swung at in the strike zone. There are more plate discipline categories than just these two, but these carry a lot of weight in respect to strikeout and walk rates, so this is a great place to start. The other good news is that these types of improvements have been shown to stabilize over a short period of time -- that is, once they show up, it doesn't take too long before we can be confident that what we're seeing is actually an improvement instead of just random noise.
To begin with, let's look at which players showed the most improvement at laying off pitches outside of the strike zone (called O-Swing %) during the second half of the season compared to the first. I've included each player's first and second half stats, the difference between them, and the second half O-Swing % minus a three-year average for each player. That final column is to try to discern whether the second-half improvement was actually real, or whether it was simply a response (regression) to a first half that was outside of the player's "normal" performance from the past three years. For players with less than three years of MLB service time, as much playing time as possible was included in the final column. Let's see our top 10 for O-Swing improvement:
| Player | 1st Half O-Swing % | 2nd Half O-Swing % | Change | 3-Year 2nd Half Change* |
| Evan Gattis | 44.2% | 30.7% | -13.5% | -12.7% |
| Yunel Escobar | 32.2% | 24.3% | -7.9% | -2.4% |
| Nick Castellanos | 37.9% | 30.1% | -7.8% | -3.7% |
| Ian Desmond | 38.3% | 31.5% | -6.8% | -4.2% |
| Shin-Soo Choo | 24.4% | 17.9% | -6.5% | -5.0% |
| Chris Owings | 41.0% | 34.6% | -6.4% | -3.2% |
| Jose Abreu | 41.2% | 35.1% | -6.1% | -6.5% |
| Yadier Molina | 38.9% | 33.0% | -5.9% | -1.0% |
| Mike Trout | 27.0% | 21.2% | -5.8% | -3.8% |
| Jason Heyward | 29.9% | 24.4% | -5.5% | -5.5% |
Evan Gattis basically became a completely different hitter in the second half of the season. Jeff Sullivan already pointed this out in September, and this should act as further confirmation: after a rough first half in which he struck out 22.4 percent of the time, Gattis showed a remarkable transformation, cutting down on the rate of swings at out-of-zone pitches by 13.5 percent. That lowered his second half strikeout rate to 16.3 percent -- better than league average -- and raised his walk rate from 3.5 percent to a more palatable 6.8 percent. These are very good signs for him getting back on track for the Astros in 2016 after a tough campaign last season.
After Gattis, Yunel Escobar showed increased aggressiveness in the early months of 2015 (taking his walk and strikeout rates in the wrong direction while doing so), but he reverted to about career norms during his second half. Nick Castellanos is an intriguing case, as he carries a great prospect pedigree and showed hints in the second half that he could be on his way to realizing his potential. He brought his walk rate up to almost league average after July by way of these O-Swing changes and contact improvements, and he could be a breakout candidate in 2016. Finally, rounding out the top five, Ian Desmond raised his walk rate to above average levels in the second half by cutting down on his swings at out-of-zone pitches, though his strikeout rate remaining close to 30 percent continues to make him one of the most volatile, boom-or-bust hitters in baseball. Jose Abreu also deserves commendation for successfully adjusting to the new pitching approach employed against him that sapped some of his effectiveness in the first half.
Now let's look at which hitters increased their rate of contact on pitches they swung at in the strike zone (called Z-Contact %). Because these are strikes, and the hitters swung, it naturally follows that we want this rate to be as high as possible. Again, I've pulled the first and second half stats, the change between them, and the second half minus three-year average for each player:
| Player | 1st Half Z-Contact % | 2nd Half Z-Contact % | Change | 3-Year 2nd Half Change |
| Colby Rasmus | 76.7% | 84.6% | +7.9% | 0.0% |
| Brad Miller | 79.8% | 87.1% | +7.3% | -0.7% |
| Mark Canha | 81.9% | 88.5% | +6.6% | N/A (Rookie) |
| Starlin Castro | 87.8% | 93.6% | +5.8% | +4.1% |
| Brett Lawrie | 80.3% | 85.6% | +5.3% | -3.8% |
| Brock Holt | 89.5% | 94.6% | 5.1% | +2.0% |
| Alexei Ramirez | 88.1% | 92.9% | 4.8% | -0.5% |
| Kevin Kiermaier | 86.7% | 91.4% | 4.7% | +4.6% |
| Eric Hosmer | 89.1% | 93.7% | 4.6% | +5.0% |
| Shin-Soo Choo | 81.1% | 85.1% | 4.0% | -0.2% |
A hitter decreasing their strikeout rate to only 29.2 percent in the second half of the season might not seem like an improvement -- unless they're Colby Rasmus. After four and a half years of his in-zone contact rate declining -- helping him achieve a whopping 34.1 percent strikeout rate in the first half of 2015 that was third-worst in the majors (min. 200 plate appearances) -- Rasmus brought his contact rate back to exactly his average 2012-2014 level during the second half. His September/October reminded us of what he's capable of when he gets hot: 8 HRs, 3 doubles, and a 173 wRC+. It's not so much that he showed true improvement in the second half, but rather he undid a lot of his bad tendencies from the first.
Brad Miller showed much of the same issue, undoing some poor plate discipline that was out of line with what we saw from him the past two years. Mark Canha -- the promising rookie outfielder for the Oakland A's -- showed much better contact rates in the second half, and he could be a 20-homer sleeper in Oakland's lineup this coming season (if he's granted close to full playing time). However, not even an increase in contact could quite get Starlin Castro back to his 2014 production, and Brett Lawrie had nowhere to go but up after he struck out 26.1 percent of the time during the first half of 2015.
Both Rasmus and Miller highlight an issue with looking only at second half performance compared to first-half performance. As we can see from the chart above, the second-half changes from each player's three-year average are all over the place, even to the point of going in the wrong direction from the improvement we'd like to see over years past. To get a different angle on who showed the most improvement in these categories, we could simply look at the players that deviated most during the second half of 2015 from what they've done for the past three years.
First, let's look at the rate of swings at pitches outside of the zone, O-Swing %:
| Player | 2nd Half Change From 3-Year Average* |
| Evan Gattis | -12.7% |
| DJ LeMahieu | -9.3% |
| Alexei Ramirez | -8.9% |
| Bryce Harper | -7.3% |
| Manny Machado | -7.1% |
| Ichiro Suzuki | -6.6% |
| Jose Abreu | -6.5% |
| Dexter Fowler | -5.8% |
| Andrew McCutchen | -5.6% |
| Jason Heyward | -5.5% |
Gattis once again leads the pack, but there are some new names on here now. DJ LeMahieu had the best year of his career at the plate (while still being slightly below average), bringing his walk rate up a few percentage points. Alexei Ramirez walked more and struck out less than he had in a few years, but not even that could make up for his loss of power and speed during 2015. And here's Bryce Harper, who, to no one's surprise, wasn't given many pitches to hit during any part of the season; he intelligently laid off most of those out-of-zone pitches in the second half, boosting his walk rate to a career-best 19 percent for the entire year. Finishing the top five, Manny Machado became the powerful, patient, superstar player we've been waiting for: he almost doubled his walk rate in 2015 over last year's career-best by learning to lay off the pitches he shouldn't swing at.
Now let's look at the most improved by contact made on swings in the strike zone, Z-Contact %:
| Player | 2nd Half Change From 3-Year Average |
| Jason Heyward | 9.3% |
| Curtis Granderson | 8.9% |
| Avisail Garcia | 7.2% |
| Josh Reddick | 7.1% |
| Jay Bruce | 6.0% |
| Didi Gregorius | 5.5% |
| Dexter Fowler | 5.2% |
| Eric Hosmer | 5.0% |
| Kevin Kiermaier | 4.6% |
| Manny Machado | 4.3% |
Many people complain that Jason Heyward doesn't hit for enough power, but he has quietly decreased his strikeout rate to just above half the league average over the past three seasons. His second-half strikeout rate was a minuscule 12 percent, and Cubs fans can look forward to a very productive 2016 from him on both sides of the ball. Curtis Granderson had his best season at the plate since 2011, transforming himself into a more patient, contact-driven hitter with power upside. A strange name on here is Avisail Garcia, whose second-half contact improvement almost certainly isn't going to fix what ails him -- which is unfortunately a lot. We knew all about Josh Reddick's change of approach early on in 2015, and it stuck around during the second half. Finally, Jay Bruce has had a brutal two years -- probably driven in some part by a lingering knee injury -- and the quality of his contact has gone down, even if the frequency of it has gone up on the pitches he's swung at in the strike zone.
This is by no means a complete look at every plate discipline category, but this look at these two categories at least give us an example of who made strides during the second half of the year in respect to their plate approach. The players included here often saw meaningful jumps in their strikeout and walk rates, and those changes often stick long-term -- giving us hope that these improvements might not get lost in the current offseason. Heading into 2016, we knew we could feel great about Heyward, Harper, and Machado. But we might want to start feeling better about Gattis, LeMahieu, and Reddick's prospects too.
