From 1909-1927, there were 7 unassisted triple plays, and, since 1992, there have been 7 more unassisted triple plays. The striking thing here is that from 1927-1992, 64 seasons, there was only one unassisted triple play. At the beginning of the century there were 7 in 19 years, about 1 every 2.71 year. In the most recent 18 years, there have been 7 for a rate of 1 ever 2.57 years. Then for the entire middle of the 20th century there was one in 64 seasons.
Here is a graph of index number of triple play versus the year in which it took place:
Does anyone have any explanation as to how this could happen? All I can think of is that it might be possible that hit and runs were more popular during the periods of high triple play prevalence, making it easier to turn one. If anyone has any thoughts on this I would love to hear them.