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A quick look at Yonder Alonso’s fly ball rate

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A few points of concern about the Mariners new first baseman.

MLB: San Francisco Giants at Oakland Athletics Kelley L Cox-USA TODAY Sports

Yonder Alonso has launched 22 home runs this year. That’s more than he’s hit during the previous three seasons combined. He’s posting career highs in isolated power, walk rate, wRC+, and fWAR this year. By any measure, the former first round draft pick is in the midst of a renaissance in his age-30 season. But as good as his overall numbers look, Alonso has been struggling at the plate recently.

A few hours before this article was scheduled to publish, Eno Sarris published a very similar article on FanGraphs about Alonso’s fly ball rate. Since he has clubhouse access and an established relationship with Alonso, his article is full of details and quotes that give us a much deeper look at Alonso’s issues. I definitely recommend reading Sarris’s account of the adjustments Alonso is making to correct his recent downturn. The rest of this article is presented as a supplement to that FanGraphs article, adapted from what was written this morning before reading Sarris’s article.

Prior to this season, Alonso had established himself as a line drive hitter with a good plate discipline profile but without the necessary power to be considered a good first baseman. But this offseason, he made some significant adjustments to his swing and his approach at the plate. He quickly became the “poster boy for the fly ball revolution.” The adjustments he made had an immediate impact as he quickly launched 14 home runs in the first two months of the season. But the next two months haven’t been nearly as productive for Alonso.

Here’s a table showing Alonso’s fly ball rate by month and a few relevant offensive stats:

Yonder Alonso Month Splits

Month FB% HR/FB% ISO wOBA
Month FB% HR/FB% ISO wOBA
Apr 49.0% 16.0% 0.235 0.364
May 57.1% 35.7% 0.500 0.487
Jun 46.9% 10.0% 0.167 0.337
Jul 32.8% 25.0% 0.216 0.339

Alonso has been struggling to elevate the ball recently. That’s affected his ability to hit for power like he was earlier in the season. Here’s another way to look at his fly ball rate, a graph of his 15-game rolling average.

That downward trend doesn’t look encouraging. In July and August, his fly ball rate has fallen back to where it sat before this season. He’s dealt with a few nagging injuries to his lower body during that timeframe so that could explain some of his problems. Sarris’s article above gives us a little more insight into what Alonso is thinking:

“Just a little bit of timing issue right now. Pitches I was hitting right I’m just missing—late, early, just missed the ball. I’ve been hitting a lot more foul balls.”

I want to quickly touch on something Sarris didn’t mention in his article—Alonso’s average launch angle. If the root of his offseason adjustments was to start hitting the ball with ideal launch angles in mind, looking at his average launch angle throughout the season should give us some more information about his missing fly balls.

Below is a graph of Alonso’s rolling average launch angle this season:

The data in this graph matches what we’d expect to see by just looking at his batted ball stats. But the little uptick in average launch angle on the far right of the graph gives us a glimmer of hope. In his past seven games, he’s hit just five ground balls and has elevated (hit a line drive or fly ball) ten balls in play. He has just one extra-base hit in those seven games but it looks like he’s finally getting his approach at the plate back on the right track.