"What are the odds?" An MLB Team Hits a Grand Slam Four Games in a Row

Last week, the San Diego Padres hit a grand slam in four consecutive games (all against the Texas Rangers) - something that had never been done before:

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A post shared by CBS Sports (@cbssports) on Aug 20, 2020 at 8:41pm PDT

As CBS Sports points out above, there have been roughly ~407,000 games in MLB history - so what were the odds that it hadn't happened yet?

I simulated each game of the Padres/Rangers series (2 in Arlington, 2 in San Diego) and estimate the probability of hitting a grand slam in each game as:

GameNum	Team	ProbGrandSlam
1	SDP	5.64%
1	TEX	2.27%
2	SDP	4.77%
2	TEX	2.16%
3	SDP	2.58%
3	TEX	1.63%
4	SDP	3.17%
4	TEX	1.54%

Multiplying each game together results in a truly unlikely series of events: 

Team	Prob4InARow	1 in...
SDP	0.000220%	454,489
TEX	0.000012%	8,124,789
Avg	0.000116%	860,825

So over the course of Major League history, it truly is unlikely it hadn't happened yet. There are slightly less four game streaks than games, since you the first three games in a season don't make a streak of four. So as an estimate, I removed 3 games per year times 117 years = 351 games, out of 407,000, gives 406,649 approximate sequences of four games in a row.

Using this San Diego/Texas series as a proxy, there is roughly a 99.999884% chance that a four game stretch does NOT have a grand slam in each game (1 - 0.000116%).

So 99.999884% ^ 406,649 four game sequences = 62.35% - the odds that this had not happened yet. Resulting in a 37.65% chance of making it this far in to MLB history without the feat occurring.

Therefore, it might be fair to guess that the baseball gods were therefore punishing the Rangers for griping about Tatis hitting the first grand slam on a 3-0 count late in a blowout.