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Wizard
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Wizard
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May 8th, 2019 at 12:26:12 PM permalink
Forgive me if we discussed this before. I know I analyzed this recently, but can't recall why or where.

I hear that William Hill offers a prop bet on a daily basis during baseball season on whether there will be at least one Grand Slam that day. In a day with 15 games, I hear the odds are close to -110 each way.

According to the Baseball Almanac, there have been 2461 grand slams in the 20 seasons from 1998 to 2017. Why start in 1998? That is the year two expansion teams were added, for a total of 30 teams. I do not know if their data includes post season games, but I'm assuming not.

Each team plays 162 games per season. So, that is a total of 30*162/2 = 2,430 regular season games per year, or 48,600 over 20 years. You divide by two because every game has two teams.

So, the average grand slams per game is 0.05064. Using the Poisson distribution, the probability of zero is exp(-0.05064) = 0.950623. So, the probability any given game will have one is 4.9377%.

The following table shows the probability of at least one grand slam over 1 to 15 games and the fair line on at least one grand slam.

Games in a Day Prob. Grand Slam Fair line Yes
1 4.94% 1925
2 9.63% 938
3 14.09% 610
4 18.34% 445
5 22.37% 347
6 26.20% 282
7 29.85% 235
8 33.31% 200
9 36.60% 173
10 39.73% 152
11 42.71% 134
12 45.54% 120
13 48.23% 107
14 50.78% -103
15 53.21% -114


Comments?
It's not whether you win or lose; it's whether or not you had a good bet.
michael99000
michael99000
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May 8th, 2019 at 12:35:27 PM permalink
Quote: Wizard

Forgive me if we discussed this before. I know I analyzed this recently, but can't recall why or where.

I hear that William Hill offers a prop bet on a daily basis during baseball season on whether there will be at least one Grand Slam that day. In a day with 15 games, I hear the odds are close to -110 each way.

According to the Baseball Almanac, there have been 2461 grand slams in the 20 seasons from 1998 to 2017. Why start in 1998? That is the year two expansion teams were added, for a total of 30 teams. I do not know if their data includes post season games, but I'm assuming not.

Each team plays 162 games per season. So, that is a total of 30*162/2 = 2,430 regular season games per year, or 48,600 over 20 years. You divide by two because every game has two teams.

So, the average grand slams per game is 0.05064. Using the Poisson distribution, the probability of zero is exp(-0.05064) = 0.950623. So, the probability any given game will have one is 4.9377%.

The following table shows the probability of at least one grand slam over 1 to 15 games and the fair line on at least one grand slam.

Games in a Day Prob. Grand Slam Fair line Yes
1 4.94% 1925
2 9.63% 938
3 14.09% 610
4 18.34% 445
5 22.37% 347
6 26.20% 282
7 29.85% 235
8 33.31% 200
9 36.60% 173
10 39.73% 152
11 42.71% 134
12 45.54% 120
13 48.23% 107
14 50.78% -103
15 53.21% -114


Comments?



Is the line always the same on every day where thereís x number of games ?

In other words, if thereís 15 games today and the line in Yes is -110, is the line -110 every time theres 15 games ?

What happens if a game is rained out or shortened by rain? Are all bets on the grand slam wager voided ?

Iím thinking of a few ideas -

1. Look at the ERAís of the 30 starting pitchers for that day. Is there a large number of bad pitchers going? You can even look at home runs allowed/inning instead of ERA for a better idea of how likely homeruns are to be hit that day.

2. Look at the home ballparks that day. Are Colorado , Philadelphia , Baltimore , Cincinnati etc playing at home? Those parks are more likely to yield homeruns.
Keeneone
Keeneone
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May 8th, 2019 at 12:40:19 PM permalink
Good stuff, and thanks for posting. I do remember reading about this somewhere on the site. I am also pretty sure mustangsally mentioned something about this topic in the past as well.

There where 3 Grand Slams yesterday, 2 in the same game.
Harper:
https://www.mlb.com/gameday/phillies-vs-cardinals/2019/05/07/566584#game_state=final,lock_state=final,game_tab=box,game=566584
O'Hearn and Merrifield:
https://www.mlb.com/gameday/royals-vs-astros/2019/05/07/565620#game_state=final,lock_state=final,game_tab=box,game=565620
TomG
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Thanks for this post from:
kuma
May 8th, 2019 at 1:24:24 PM permalink
-First thought was that 1998 was right in the middle of some of the greatest offensive output in history. Although we want as much data as possible, conditions in sports are constantly changing.
-Next thought is that while scoring was down recently, homeruns are now way up, so perhaps the chances of a grand slam are still the same, possibly even higher than ever
-Wind blowing out in Wrigley could be factor, as could some bad starting pitchers for the day. A fame in Colorado would have an effect to the yes, and one San Diego probably a slight effect on the no.
-With only 2461 four-run homeruns out of more than 50,000, getting the bases loaded is probably a bigger factor. If I was going to handicap this, after weather, I would look at the walk rates of the starting pitchers for the day. High lean toward yes, low lean toward no. And if I could beat (or maybe only come close) to the historical fair line, it would be a good bet. Probably be more likely to find something good on Mondays and Thursdays when there are fewer games
7craps
7craps
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May 8th, 2019 at 1:31:51 PM permalink
Quote: Keeneone

There where 3 Grand Slams yesterday, 2 in the same game.

The average I see the last 3 years is 1 in 18.5. This year so far stands at 1 in 18.48 (4 games played so far today)
So players, during the last playoffs, IIRC, mentioned the baseball seemed different. No wonder home runs are up.

the last few days saw an explosion of GS.
4-May cubs,atl			
5-May sea, hou, sd, cubs, bos
6-May bal, tbay
7-May kc, phil, kc
8-May TODAY so far tex
12 in 4 days AFTER 6 days in a row with 0.

The william hill odds are always different, depending on how many games are scheduled that day. I have never seen a line for 10 or less games.
here is a sample of this year so far
yes|no
+105|-125
-115|-105
+120|-140
+120|-140
+130|-150
+110|-130
-120|-100
+105|-125
+115|-135
+115|-135
even|-120
even|-120
-115|-105
+115|-135
+110|-130
-105|-115
even|-120
-105|-115
-110|-110
+110|-130
a couple years ago, the odds for yes averaged +135. no longer
as more GS are hit each year.
some data is found here: https://sites.google.com/view/krapstuff/mlb
Last edited by: 7craps on May 8, 2019
winsome johnny (not Win some johnny)
Wizard
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Wizard
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May 8th, 2019 at 2:10:10 PM permalink
Quote: Keeneone

Good stuff, and thanks for posting. I do remember reading about this somewhere on the site. I am also pretty sure mustangsally mentioned something about this topic in the past as well.



Yes, thanks, that is who wrote to me about this. As I recall, I argued that in general neither side was good, but am not sure she agreed.

Here is the number of Grand Slams in the 20 years I'm looking at:

Year Grand Slams
1998 120
1999 139
2000 176
2001 134
2002 125
2003 123
2004 133
2005 132
2006 134
2007 136
2008 124
2009 137
2010 124
2011 98
2012 101
2013 95
2014 83
2015 108
2016 107
2017 132


2000 was the a big aberration with 176.

Does anyone know how many there were last season?

As to the pitchers and stadiums, I tend to think the market adjusts for those things. Over 15 games, it probably averages out fairly well.
It's not whether you win or lose; it's whether or not you had a good bet.
7craps
7craps
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May 8th, 2019 at 2:31:49 PM permalink
Quote: Wizard

Does anyone know how many there were last season?

Here is what I collected (seasons checked each 3 times by 3 different people using mlb.com and espn.com)
2017: 133 total grand slams hit in 130 games with at least 1 GS (3 games had 2 hit)
2018: 134 total grand slams hit in 132 games with at least 1 GS (2 games had 2 hit)
2019: 31 total grand slams hit in 29 games with at least 1 GS (2 games had 2 hit)

when I do watch MLB games, it is surprising to me how many times the bases are loaded over 15 games played.
winsome johnny (not Win some johnny)
Ayecarumba
Ayecarumba
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May 8th, 2019 at 2:38:53 PM permalink
The thread title "Gland Slam prop bet" made me think this was a new WoV Spring Fling challenge.
Simplicity is the ultimate sophistication - Leonardo da Vinci
TomG
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May 8th, 2019 at 2:48:53 PM permalink
Quote: Wizard

As to the pitchers and stadiums, I tend to think the market adjusts for those things. Over 15 games, it probably averages out fairly well.



Possibly. But because they are so few grand slams, any day-to-day differences almost certainly follow expected runs scored and nothing else. Which for a small and not widely available market might be distorted. Be interesting to see how closely the grand slam odds correlate with the grand salami odds
7craps
7craps
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May 8th, 2019 at 3:19:59 PM permalink
Quote: Wizard

I hear that William Hill offers a prop bet on a daily basis during baseball season on whether there will be at least one Grand Slam that day.

That is true. I wagered on that bet last Sat and won
Quote: Wizard

So, the average grand slams per game is 0.05064.

I think to be more accurate, some games have more than 1 grand slam hit. you need to subtract them from the total hit and then finish the math.

That stumped me a few years ago.
winsome johnny (not Win some johnny)

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