What happened to Alex Wilson?

Since being acquired along with Yoenis Cespedes from the Boston Red Sox prior to the 2015 season, Alex Wilson has become a staple in the Detroit Tigers’ bullpen. He’s been a staple that has both literally and figuratively held together what has been one of the most fragile bullpens in all of baseball for quite some time. He has truly been an unsung hero who hasn’t received as much praise as he’s earned.

Just to put Wilson’s contributions for the Tigers in perspective, he’s pitched at least 70 innings each of the last two seasons which puts him 11^th among all relief pitchers in terms of total innings over that time. Over the same period of two seasons, Wilson is number 23 in earned run average among 92 relievers who’ve pitched at least 100 innings between 2015 and 2016, and he’s 17^th in adjusted earned run average among the same group.

From those numbers alone it’s safe to say Wilson has been one of the more reliable relief pitchers in the league and undoubtedly the best in the Tigers organization since being acquired. We’ve grown accustomed to a reliable and consistent performer each and every day — and often it was every day.

Now the 2017 season started out much the same as his previous seasons with the Tigers. By the end of May — a rollercoaster of a month for the Tigers’ bullpen that saw Francisco Rodriguez completely implode to epic proportions at the beginning of the month only for Justin Wilson to take the reigns as closer and also somewhat struggle — Wilson emerged as the best of the Tigers back end bullpen again, this time alongside Shane Greene who’s much improved this season.

By the end of that dumpster fire of a month for the rest of the Tigers’ bullpen, Wilson had an ERA under two, a batting average against (BAA) of .182, and a walk rate slightly under seven percent. This put him among the top echelon of relief pitchers two months into the season.

However, that all changed the next month as Wilson had a terrible month of June — one of his worst ever, in fact. Out of the 15 earned runs he’s allowed this season, 10 came in the just under 10 innings of work during June, which ballooned his ERA from a respectable 1.88 all the way up to over four. Also during the month of June came 19 of the 35 total hits Wilson’s allowed this season, where batters hit .422 off him and had a staggering OPS (on-base plus slugging) of 1.158.

What caused one of the most reliable relief pitchers in the game to turn into one of the least reliable? In a game of inches, it doesn’t take much. The heatmaps below tell us the same thing as they show the location of Wilson’s hard pitches, his two-seam and four-seam fastballs along with the cutter. The first heatmap on the left shows those three hard pitches’ during April and May of this season. The second heatmap shows the location of the same three pitches during the month of June.

Baseball Savant

You can see a big difference especially how far their location has moved down in the strike zone. Coincidentally this is where the singles, doubles, triples and home runs have come, as the heatmap below shows the location of all three pitches that resulted in a base hit during the month of June which is exact location where Wilson began throwing more of his hard pitches in the same month.

Baseball Savant

This tells us that hitters know he’s throwing the hard pitches lower. They have adjusted and are now looking for that spot. When all three are the same speed it’s easy to sit on all three of them with little adjustment. Further evidence of how much success hitters had in June is a table below showing the batting averages and slugging percentages against each of Alex WIlson’s four pitches.

In order to return to how successful he was in April and May, Alex Wilson needs to adjust where he’s primarily locating those three hard pitches back to where they were during the first two months of the season: higher up in the strike zone. If he’s able to do that we should see a strong finish in the second half for him, regardless of how the Tigers finish in the standings. Alex is arbitration eligible until 2020 so we’ll have a reliable arm out of the bullpen during the likely rebuild .