How Rare Are Triple Plays?

According to NESN, tonight's was the 30th triple play in Red Sox history.

To put that in perspective, the team is well over 100 years old. For the last 50 years, the season has been 162 games. Call the 50 years before that (just go with it) 154 games, and that means 15,800 games (158 being the average, times 100). Multiply that by nine, and you have 142,200 chances for a triple play.

Divide 142,200 by 30, and you have one triple play every 4,740 innings.

That's pretty rare.