Fastballs
Defensive shifts have been around a very long time. Teams used to shift against Ted Williams way back in the day:
.235

More strikeouts and fewer balls in play

.274
Seems counterintuitive, right? Pitchers are using their fastball less despite throwing harder than ever. Seems like you’d want to throw your fastball more when you have this much velocity, but that hasn’t happened. Teams are scaling back on the heater.

Strikeout rate Walk rate Plate appearances that end with a ball in play
Sliders Sliders Sliders Sliders Sliders 72.4% 8.5% .297

The 2010s are the first decade with pitch tracking fully available. PitchFX launched in 2007 and was fully available for the first time in 2008. Statcast and Trackman have since taken the reigns. The data confirms two things. One, pitchers are throwing harder than ever. I mean, duh. We all knew that. And two, pitchers are throwing their fastballs less than they were 10 years ago.  2019
58.3%