For most of his baseball career, Xander Bogaerts has been an extremely successful player, whether it’s been in the low or high minors. He’s also always been a highly touted prospect, primarily praised for his ability to hit the baseball all the while playing reasonably good defense as a shortstop. It’s not simply his ability to impact the baseball that made him such a touted prospect, but also his approach. In his brief stint in the majors, in 2013, Bogaerts was lauded for his impeccable plate discipline, especially in the playoffs. As he should, as he had a 10% walk rate in 2013, and in the postseason it skyrocketed to 17.6%.

This, however, was in a small sample size; Bogaerts only had 50 plate appearances in the majors in 2013, and only 34 in the playoffs. In 2014, he got off to a very strong start. He didn’t hit for much power at the beginning of the year but he walked an awful lot and the power was slowly starting to creep up. Around the end of May, he had close to a 400 OBP.

But the wheels fell off after that. Bogaerts simply stopped walking and hitting well. He basically struggled the rest of the year apart from September, when he did show signs of improvement. Bogaerts’ failures though went almost side by side with his walk rate apart from the last month of the season where he did have a spike in BABIP. Below is a chart of his walks per month displayed by Baseball Savant.

As you can see Bogaerts walks just took a huge dip after May. So what happened? Why did he just stop walking? Well there are a number of factors to consider here. First I think it’s important to look at how he was pitched, did pitchers make a sudden adjustment? Below is a chart of hard, breaking, and off-speed pitches used against him in 2014. Provided by Brooks Baseball.

What is primarily noticeable is that pitchers, as the year went on, started throwing fewer hard pitches and more breaking pitches. This, however, only shows us that pitchers made an adjustment to him. It doesn’t show us the full story; it doesn’t show us how he reacted to the adjustments the pitchers were making.

There are many factors that can indicate how a player reacts to pitching adjustments. We can look at his swing rate or his whiff rate but the question, which we are really trying to answer, is did something change in the player’s approach? Below I think is the most accurate example of how Bogaerts changed his approach at the plate and why he started walking a lot less. It’s a chart provided by Brooks Baseball that examines a player’s aggressiveness and passiveness, essentially his plate approach on hard, breaking, and off-speed pitches.

As you can see, Bogaerts was a very patient hitter early on in the year, but as the season went on he became increasingly aggressive at the plate. In fact, he didn’t just start getting more aggressive on one type of pitch, but in general. He went away from what made him successful on the outset and began his prolonged slump throughout the year. What can be rather alarming is that it wasn’t just a one- or two-month spike in aggressiveness, but rather a trend in increased aggressiveness throughout the year.

Xander Bogaerts is still a very young player — he’s going into his age 22 season — and this breakdown by no means should be taken as a prediction for future failures. This is really just part of maturing as a young player, getting better and making adjustments. He went through the highs and lows of a baseball season in 2014. While I don’t expect him to be a superstar next year, I do expect that we will see significant improvement in not just his stats but his approach at the plate. My advice to him would be to look back at what made him successful in the first two months of the 2014 season and try to replicate that. Don’t be so aggressive at the plate, just wait for your pitch and when you get it, put a good swing on it. This is of course an annoying cliché but I do think it applies in his case.