Yankees letter from Rob Manfred reveals team engaged in video sign-stealing before MLB crackdown in 2017
Sign of times: Major League Baseball gives OK to electronic pitch calling
Commissioner's 2017 Letter to the Yankees on Sign Stealing - The New York Times
Notable suspensions and discipline in baseball history
Sign stealing - Wikipedia
Yankee letter,' explained: What's revealed in early release of letter by MLB commissioner Rob Manfred
Astros, Red Sox sign-stealing timeline: Everything we know about MLB scandals
Sign stealing, The Baseball Codes
MLB letter to New York Yankees detailed illicit use of technology prior to 2017 sign-stealing edict - ESPN
In Astros Inquiry, Rob Manfred Raises Possibility of Big Penalties - The New York Times
Sign stealing in MLB isn't new