First Inning Home Field Advantage

The home team has consistently, on a year-to-year basis, won 54% of its games. Several reasons have been explored for the disparity, such as familiarity to the home field and the umpire’s biased strike zone. Another aspect that comes into play is a first-inning discrepancy in favor of the home teams’ pitchers. They have an abnormally large advantage in strikeout and walk rates, partially because of a higher fastball velocity.

Note: For consistency throughout the article, when I refer to K/BB, it will be in reference to pitchers.

With better use of bullpens and more patient hitters, strikeout and walk rates have climbed in recent years. Since 1950 (the extent of Retrosheet’s data set), the home team has always maintained a higher K/BB ratio than the away team.

While the strikeout portion of K/BB has outpaced the walk portion, the ratio of home K/BB to away K/BB has remained fairly constant — averaging 1.14 and bouncing between 1.09 and 1.19. While trying to remove some of the noise from the data, I figured I would remove the ninth inning, when the away pitcher doesn’t always pitch. While looking at inning-by-inning data, I found the first inning exhibited the greatest K/BB ratio, compared to other innings.

Usually, the first inning is a little rougher for pitchers since they are guaranteed to face the top of the other team’s lineup. The second inning sees the highest K/BB values since the pitcher usually faces the bottom part of the lineup. After the second inning, the order become fairly random.

The ratio was at 1.3 for the first inning, then declined as the game went went on to a low of 1.07 for the ninth inning. I know some people prefer K% and BB%. The K%-BB% for the home team was 6.8% in the first inning and 3.6% for the away team (3.2% total difference). By the ninth inning, the total difference was .5%

While reading many articles on this subject I came across this little tidbit, from our own Matt Swartz, while he was at Baseball Prospectus:

That first-inning differential is particularly interesting, because it could be caused by another factor. Instead of the issue being that the home pitcher was more familiar with the mound than the visiting pitcher, perhaps the home pitcher is just more prone to be more effective immediately after warming up. Maybe a home pitcher knows the exact moment that he is going to step on the mound and can warm up until a couple minutes beforehand, and maybe a visiting pitcher loses focus and cools off while in the dugout waiting for his team to finish batting in the top of the first inning before getting the ball. While first warning readers about the small sample size, I can now say that we do see some clear indications that the first-inning warm-up effect may be part of home-field advantage.

Could it be the away pitcher just sits too long? Normally, the starting pitchers join their teams for the “The Star-Spangled Banner.” Then, the home starter takes the mound. The away team’s starter heads to the dugout for his warmup jacket. Here are the average per inning fastball and sinker speeds, since 2007.

Note: I only looked at the first five innings in order to minimize the effect of relievers entering the game.

In the first inning, home starters averaged a fastball .15 mph faster than their away counterparts. The difference increased to .19 mph if the away pitcher’s team scored any runs thereby extending the time he was on the bench. Here is a chart on how fastball speed declined as the starter waited longer for his team to finally quit hitting.

The decline became significantly pronounced once the away team made the starting pitcher wait five minutes or more for runs to be scored.

So the home starter throws harder to begin with — but does this difference in velocity really matter? The short answer is no. It makes a nice difference in the first inning, but as the game goes on, the away team actually sees a very slightly higher velocity. Going back to the original question of home field advantage — and using some of Mike Fast’s previous work — higher velocity ends up explaining one run of the home field advantage over an entire season.

While the difference is not huge at the league level, it’s more pronounced at the pitcher level. Here are the 11 pitchers who have seen a one mile-per-hour-or-more drop in velocity between throwing in the top of first inning compared to the bottom of the inning (2013 data, minimum 1,000 fastballs thrown)

Name Top of the 1st Bottom of the 1st Difference
Hyun-Jin Ryu 91.0 89.4 1.6
Corey Kluber 94.4 92.9 1.5
Mark Buehrle 83.8 82.4 1.4
Joe Blanton 89.7 88.3 1.4
John Danks 89.3 88.1 1.2
Kyle Kendrick 89.6 88.4 1.2
Julio Teheran 92.4 91.2 1.2
Dan Haren 87.5 86.4 1.1
Yu Darvish 92.4 91.4 1.1
Jered Weaver 87.8 86.8 1.0
Ervin Santana 93.0 91.9 1.0

Some home teams should allow certain starters to go back to the bullpen to finish their pregame warm ups while his teammates are batting. This may cause a little problem in the National League — where the pitcher might end up batting — but if a pitcher is hitting in the first inning, the inning has been a good one. I think the team could plan on using the time the home starter warms up to start the inning and set some time to account for the first three batters. Once this second warm-up is complete, he could then venture to the dugout.

Over the years, the home team has an advantage in the first inning when it comes to the team’s pitchers throwing more strikeouts and allowing fewer walks. Part of the advantage can be attributed to the home pitcher having less time to cool off. The longer the pitcher sits, the slower they seem to throw when they finally take the mound. While the velocity loss from sitting in the dugout does not explain all the difference in strikeout and walk rates, it is a factor. Additionally, the drop off is larger for some pitchers than for others.

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Jeff writes for FanGraphs, The Hardball Times and Royals Review, as well as his own website, Baseball Heat Maps with his brother Darrell. In tandem with Bill Petti, he won the 2013 SABR Analytics Research Award for Contemporary Analysis. Follow him on Twitter @jeffwzimmerman.

12 Responses to “First Inning Home Field Advantage”

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  1. tz says:

    Could also be home cooking vs. hotel cooking. Seriously, because starting pitchers are creatures of routine there’s less chance of having their pre-start routine interrupted by poor sleep, indigestion, etc.

    (This may also explain why Aroldis Chapman is best left in the pen. Too much of a sweet tooth).

    Great stuff as usual Jeff.

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  2. rageon says:

    This was excellent. Thanks.

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  3. Jon Roegele says:

    Really enjoyed this Jeff, great idea for a study. I’d noticed in the past that on the whole, the away team tends to throw slightly harder too, which I find interesting. I also found that if you take into account average fastball speed per base-out-count state, pitchers actually throw slightly slower in the first innings and peak around pitch 40-65. It’s cool to see this in an absolute sense and your thinking behind the first inning differences.

    As far as your list of starters that show the largest first inning home/away velocity deltas, I believe some of this is just home park effects. I just looked at these the other day, and all but Darvish of your list would tend to be helped by home PITCHf/x park effects. I can certainly believe the effect you describe would be real though – this is just another effect.

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    • ReuschelCakes says:

      do we park effect velocity now?

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      • Skin Blues says:

        We absolutely should park effect velocity. I remember reading that article a couple days ago, and it seemed that it would be hard to get an overall number for park effect over the course of a season due to effects of temperature, weather, recalibration, etc. I would certainly not put a lot of weight on individual pitchers’ Home v Road velocity splits, it’s just so hard to know how to adjust them to be anywhere near accurate.

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    • Jeff Zimmerman says:
      FanGraphs Supporting Member

      I will go through the list tonight (once I can see my original data) and see who moves up and down.

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      • ReuschelCakes says:

        But I thought Jon himself conceded that these differences change over the course of the year. If healthy front-line starters have had ~15 starts both home and away, we are talking incredibly small sample sizes that would be vulnerable to situational, weather and fluid park effects, no?

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  4. chuckb says:

    Fantastic stuff. One problem that might occur with some teams having their pitcher warm up in the top half of the inning is that they also often like to have their starter warm up with their starting catcher. Though the pitcher probably won’t bat in the top half of the 1st, it’s more likely that the catcher will. So they may be unwilling to give that up in order to have the starter finish his warm up in the top of the 1st.

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  5. brett says:

    Great work Jeff. I didn’t read the linked article about umpires, so maybe it’s covered in there, but could this be about them as well? I imagine it takes time for umpires need to settle into a game and find their strike zone for the day. Maybe increased nerves and uncertainty in the first inning lead to a greater home team bias?

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  6. Peter Jensen says:

    The decline became significantly pronounced once the away team made the starting pitcher wait five minutes or more for runs to be scored.

    Or it could be that the Away starting pitcher doesn’t feel the necessity of having to throw his fastest pitches when he already has a lead of 5 or more runs.

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  7. Rick says:

    One issue for having a visitor pitcher warm up in the pen during the first inning may be that it’s against the rules. Off the top of my head, haven’t looked it up, but don’t the rules state that a pitcher cannot warm up in the pen once he’s entered the game if it would take unusual time for him to go to and from the pen. This would mean any bullpen that’s not on the field would be against the rules to warm up in if you’re listed in the starting lineup
    (especially for NL games where the pitcher could hit in the first inning).

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  8. Gyre says:

    4% is nothing. Don’t you guys EVER look at std dev to find out the scattering?

    4% is about the number of times sudden death kicks in and the Visitors do not get to bat again.

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