Why are MLB playoff teams launching so many first inning home runs? The answer may be deceptively simple

Greg Eng

Baseball saw an explosion of home runs during the 2017 season as MLB set a new record for total round trippers in a season. Twelve games into the playoffs batters have followed that trend, but at a peculiar time. If you watched many of the games thus far, you noticed the majority of home runs in the postseason have come during the first inning. In the past five years, there have been 35 homers in the opening frame of playoff contests. This year, there have been 13 home runs in the first inning and there are still games to be played in the first round division series.

What makes this year different? There are plenty of theories, but just one common theme: It's all connected with the starting pitching. Starters are not getting off to the same success as in prior years. Even the great pitchers like Chris Sale and Luis Severino couldn’t get through the first inning without letting up a home run this year. Not only did they let up one, but those aces let up two! Comparing these statistics to those from the prior five seasons, there’s a clear pattern.

For a deeper examination of the trend, let's look at the data. From 2012 to 2016, the home runs by year go as follows; five, two, six, 15, and seven. Clearly, the trend is that there are more home runs hit in general and more coming in the first inning. But when you really break it down further, it can be separated into these three factors: pitch number, pitch count, and home field advantage.  

The pitch number: When a pitcher comes in the first inning, they want to find their groove and start with a lot of strikes. A first strike is key in an at-bat because it puts a batter in a hole. In the past five years, home runs on pitches early in the count (first four pitches) have steadily increased each postseason. They have risen each year from 50 percent to 60 percent to 80 percent ... or even higher. So far this season, 82.85 percent of home runs have come on pitches early in the count. This means hitters are being aggressive early because they know the pitcher is going to more likely to deliver a strike. If you knew early in the count that you were eventually getting a pitch over the heart of the plate, it’d be easier to hit a home run when that pitch arrived.

The pitch count: This year in particular, first pitch fastballs aren’t recommended. As shown above, when you try to get ahead early in the count, batters tend to punish pitchers. Well, pitchers can learn too. Pitchers typically started batters with breaking balls and changeups to try and throw off the man at the plate. The problem came when they fell behind in the count if and when the batter didn't bite. In the past five postseasons, home runs came when the batter was ahead in the count 12 times, behind in the count 16 times, or even in the count seven times. Batters were biting, and thus pitchers were ahead in the count and able to do more damage with pitch mixes. Thus far in 2017, batters were ahead in the count for 12 of the 13 home runs, with the other one being Jose Altuve's Game 1 shot when he was down 0-2 in the count. It’s simple: when batters have a count that favors them, they’re able to swing without the fear of striking out and really swing for the fences.

Home or away factor: Home field advantage is a real advantage when it comes to the playoffs. We saw in Game 5 of the 2015 ALDS series between the Blue Jays and Rangers how a home run can make a stadium go crazy and completely change a series, in the Jose Bautista bat flip game. In particular, this postseason has been very kind to teams playing on their home field. Of the 13 home runs thus far, 10 came at home. In the past five years, 18 of the 35 came at home, a mark of just more than 51 percent. Fans are electrified in the first inning of games, as they should be, and players use that energy to fuel their adrenaline to hit the long ball.

There could be other theories as to why there’s been a spike in home run balls in the first inning, but from an analytic standpoint the reasons are clear. Hitters are aggressive early, pitchers fall behind in the count, and a home field advantage all equal more home runs in the first inning. It’ll be fun to see how managers adjust pitching strategies entering a game moving forward. Who knows, maybe they’ll start relievers first and go to their starters in the second inning. Based on the current home run rate in the first inning, it would be hard to fault them. You never know in the game of baseball.

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