With three seasons of Statcast™ in the books, a hitter's improvement now can be judged on more than just his end results.
An increase in home runs or OPS is great. But Statcast™ opens a window to the quality of his contact. Did he hit the ball harder, lift it in the air more -- or best of all, both?
With that in mind, MLB.com studied a group of more than 200 hitters who produced at least 200 batted balls in both 2016 and '17 to see who improved the most in each of four important categories. Here are the results:
Average exit velocity

1. Jed Lowrie, A's: +3.1 mph (85.7 to 88.8)
   
2. Carlos Gomez, Rangers: +2.2 mph (85.3 to 87.5)
   
3. Bryce Harper, Nationals: +2.0 mph (88.6 to 90.6)
   4 (tie). Brandon Moss, Royals: +1.7 mph (87.9 to 89.6)
   4 (tie). Luis Valbuena, Angels: +1.7 mph (85.6 to 87.3)
   What a difference good health makes. As a 33-year-old, Lowrie's games played jumped from 87 to 153 and his OPS from .637 to .808 as he finished second in the Majors with 49 doubles. The second baseman saw his average exit velocity rank (minimum 200 batted balls) soar all the way from 234th to 74th -- essentially tied with Michael Trout and Justin Upton.

Gomez, a free agent for the second straight offseason, recovered from a rough stint in Houston. After averaging 87.2 mph with the Brewers over the first four months of 2015, that number plunged to 84.4 mph for the Astros from the '15 Trade Deadline deal until his release in August 2016. Gomez improved his average to 88.6 mph after Texas picked him up, and he carried some of that improvement into this year.
Harper, enjoying a big rebound year until a mid-August knee injury, saw his exit velocity bounce almost all the way back to its 2015 level (91 mph). The Nats slugger finished 14th in that category in '17 (minimum 300 batted balls) and second among left-handed batters.
Average launch angle

1. Yonder Alonso, A's/Mariners: +9.1 degrees (10.3 to 19.4)
   
2. Lowrie, A's: +7.3 degrees (11.3 to 18.6)
   
3. Gomez, Rangers: +6.7 degrees (8.3 to 14.9)
   
4. Francisco Lindor, Indians: +6.0 degrees (7.7 to 13.7)
   Three players tied at +5.5 degrees
   Although he didn't maintain his early-season heights, Alonso still hit more home runs (28) than in the previous four seasons combined (25 in 440 games), all while heading into free agency. Thanks to a swing change, his slugging percentage increased from a paltry .376 over that span to .501 in 2017 -- even with a minimal increase in his exit velocity.
   It's notable that both Lowrie and Gomez paired hitting the ball harder with hitting it higher, as those two factors both hold a great deal of importance when it comes to doing damage at the plate. So it's no surprise these two raised their isolated power (ISO) number by a combined 166 points.

Lindor more than doubled his home run total, to 33, as his launch angle continued to rise from 3.8 degrees in 2015. The Cleveland shortstop notched a hard-hit line drive or fly ball on 24 percent of his batted balls in '17, up from 17.6 percent the year before.
Hard-hit rate (95+ mph exit velocity)

1. Lowrie, A's: +12.7 percent (24.5 percent to 37.2 percent)
   
2. Scooter Gennett, Reds: +10.5 percent (25.1 percent to 35.5 percent)
   
3. Brandon Belt, Giants: +7.4 percent (33.4 percent to 40.9 percent)
   
4. Brett Gardner, Yankees: +7.0 percent (24.0 percent to 31.0 percent)
   
5. Yadier Molina, Cardinals: +6.4 percent (27.9 percent to 34.3 percent)
   Lowrie, Gennett and Gardner all had a lot of improvement after ranking in the bottom 10 percent in this category among 275 hitters who put at least 200 balls in play in 2016. Lowrie, once again, did the most climbing, as he wound up among the top 40 percent of hitters in '17.
   Gennett nearly doubled his previous career high in homers (27), with four of those coming on hard-hit balls during a spectacular performance against the Cardinals on June 6. Meanwhile, Gardner tripled his homer total (a career-high 21), while going 9-for-12 with three doubles and four home runs on balls hit 105 mph or harder.

Belt ranked 17th of 102 left-handed hitters in hard-hit rate in 2017 (minimum 250 batted balls), and eighth in the same group with a .379 expected wOBA, which factors in the quality of a player's contact. Unfortunately, the first baseman sustained a season-ending concussion in early August, limiting him to 451 plate appearances.
Barrel rate

1. Randal Grichuk, Cardinals: +5.9 percent (9.8 percent to 15.7 percent)
   
2. Alonso, A's: +5.8 percent (4.1 percent to 9.9 percent)
   
3. Ryan Zimmerman, Nationals: +5.7 percent (7.0 percent to 12.7 percent)
   
4. Eduardo Escobar, Twins: +5.4 percent (3.2 percent to 8.5 percent)
   
5. Logan Morrison, Rays: +5.3 percent (7.5 percent to 12.8 percent)
   Lots of strikeouts and few walks are issues for Grichuk, a potential trade chip for St. Louis this offseason. But when he makes contact, he frequently produces barrels -- batted balls whose combination of exit velocity and launch angle make them ideal for doing damage. Just seven of the 284 hitters to put at least 200 balls in play this year created a barrel more often, an exclusive list that includes Aaron Judge, J.D. Martinez and Giancarlo Stanton.

At age 32, Zimmerman recovered from a miserable 2016 by rocketing from 120th to 23rd in MLB in barrel rate (minimum 200 batted balls). While the veteran was hitting the ball hard in '16, he also increased his average launch angle on hard contact from 8.1 degrees to 13.2 degrees.
Like Alonso, Morrison enjoyed a breakout, power-packed season heading into free agency. On his way to 38 homers, the first baseman more than doubled his average launch angle on hard-hit balls, from 9.3 degrees to 18.9 degrees.