I recently purchased the play index feature from Baseball-Reference. Holy cow is this a lot of fun to play with.
I wanted to get under the hood and think of how this tool can help me on this blog. I got to thinking about balks.
The most common balk is the “no stop” balk. Here is an example from opening day:

Here is the last part of rule 8.01(b)
The pitcher, following his stretch, must (a) hold the ball in both hands in front of his body and (b) come to a complete stop. This must be enforced. Umpires should watch this closely. Pitchers are constantly attempting to “beat the rule” in their efforts to hold runners on bases and in cases where the pitcher fails to make a complete “stop” called for in the rules, the umpire should immediately call a “Balk.”
Umpires were told to strictly enforce the no stop rule in the ’80s. I could not remember the exact year. In messing with the play index, it became clear.
I ran a report on pitchers who balked more than 10 times in a season. This has happened 13 times in history (at least the history Baseball Reference has…which is quite a lot).
11 of those 13 happened in 1988. It happened once in 1989 and has not happened since. My keen deductive skills tell me 1988 was the year of renewed focus on the rule.
This is the type of balk that most coaches understand and try to get the umpire to call. The rules only dictate the pitcher make a complete stop. It does not say for how long. The rule of thumb is to make sure the arms and legs are not moving at the same time. If this does not happen, there had to be a stop in there somewhere.
This type of balk is covered on page 23 of RuleGraphics.