On June 21st MLB umpires began inspecting pitchers for the use of foreign substances, long illegal but unofficially tolerated until recently.
The crackdown has had an impact on overall batting statistics, perhaps not as dramatic as some would have expected, but still significant.
League Batting Stats Before and After the Crackdown on Foreign Substances
Some pitchers have seen dramatic declines in performance. Gerrit Cole’s ERA before the crackdown was 2.31. In the three games since it is 6.46 with an xFIP of 4.59, almost two runs higher than before the crackdown. His overall fastball spin rate since the crackdown has declined almost 180 RPM, from 2533 to 2353.