Then there was Lagares’s launch angle, which is the vertical angle at which a ball leaves a player’s bat. The rule of thumb is that any ball struck at less than 10 degrees is a ground ball, any ball between 10 and 25 degrees is a line drive and anything between 25 and 50 degrees is a fly ball.
In 2017, Lagares’s launch angle dropped from 12.3 degrees in 2016 to 8.5. And that figure was way below the average in baseball in 2017, which, according to MLB.com, was nearly 12 degrees.
Which meant Lagares may have been pulling the ball more last season, but too many of the balls he hit were bouncing in the infield, to little effect. Indeed, his ground-ball rate rose from about 42 percent in 2016 to nearly 51 percent last season, according to FanGraphs.com. His fly-ball rate dropped to a career-low 29 percent.
Source: James Wagner, New York Times
Article includes a couple of more hitters helped by these hitting coaches, along with Lagares talking about wanting to hit 50 HR.