What the A’s Have Done With Mike Fiers

A few weeks ago, when the A’s traded for Mike Fiers, I couldn’t think of anything worthwhile to say. It’s not that I thought it was a bad move — it’s that I thought it was a boring move, an unremarkable move. A very modest rotation upgrade that would be hard to dress up for FanGraphs readers over 900 words. I tried — I dug into all the familiar statistics and websites — but nothing jumped out. The Mike Fiers trade, to me, belonged in the same transaction category as the Aaron Loup trade. It was a move that happened that I didn’t need to analyze.

Fiers has started three times for the A’s. The A’s have won all three games, and Fiers has allowed three runs over 18.1 innings. Even more, he’s allowed only one walk, while racking up 21 strikeouts. In a short amount of time, Fiers has made himself remarkable. He’s done enough to draw my attention again. When a player goes on a hot streak, it’s natural to wonder what might be different about him. Sometimes — many times — a hot streak is just a hot streak. Fiers, though, has indeed made a few tweaks. Understanding it’s always impossible to conclude that a given tweak has directly led to greater success, let’s take a look at how Fiers has changed since getting to Oakland.

There was one quote that stuck in my brain. Here’s an excerpt from an article about the trade when it was made:

“There’s some things we’ve looked at with his repertoire that will play well in our park,” [David] Forst said. “The walk numbers are outstanding. There’s a cutter and changeup that have played really well of late and we look forward to setting up a pitch plan for him.”

It’s all perfectly good, but my brain zoomed in on the “pitch plan” part. What’s implied is that the A’s were going to take Mike Fiers, with all of his preexisting stuff, and then have him maybe change a few things. Instead of just letting Fiers pitch like Fiers, the A’s would have him pitch like the Oakland version of Fiers. Forst didn’t get any more specific than that, but it’s still a tip-off. It’s a tip-off that the A’s were looking to be strategic. And there’s evidence to back up the suggestion that Fiers almost immediately made subtle adjustments.

To be clear, Fiers has been great, but this isn’t quite uncharted territory. Here’s how his K-BB% has progressed over time as a starter in the bigs:

This is a high spike. There have been other high spikes. All those spikes dropped off. So will this one; Mike Fiers, presumably, hasn’t turned into the best pitcher in baseball. It’s more a question of whether he’s improved, and, if so, how he’s improved. This is where we get to the adjustments.

Why don’t we begin with Mike Fiers’ four-seam fastball? It’s hardly an overpowering fastball, but it’s a rising fastball, and since joining the A’s, Fiers has aimed it higher than he used to. On the left, Fiers’ four-seam fastballs before the trade. On the right, after the trade.

Fiers already threw his four-seamer higher than average, but over his past three games, he’s thrown it almost exclusively in the upper half. To look at this a different way, I made use of Baseball Savant. I looked at everyone’s average four-seam vertical locations through August 1, and then I looked at everyone’s average four-seam vertical locations since August 2. Here are the ten biggest positive changes:

Fiers is fifth, out of 202 pitchers. His average four-seam fastball has ended up more than five inches higher than it did before. No one in baseball, in fact, has thrown a higher average four-seamer since August 2. It could be a coincidence, or it could’ve been Fiers’ own idea, but he’s been trying to keep that fastball above the hitters’ bats. I’m sure you’ve read enough about high fastballs over the past few years. What makes this all the more interesting is what else Fiers has done.

This is an example of Fiers’ four-seam fastball:

He also has a big, looping curveball. This is an example of that:

In the previous table, we looked at the biggest positive changes in four-seam fastball height. Now let’s look at the biggest negative changes in curveball height:

Fiers is second, out of 119 pitchers. His average curveball has ended up more than five inches lower than it did before. To put this together, on average, Fiers has increased his four-seam/curveball separation by more than ten inches. Which is, of course, almost a foot. Here’s where Fiers’ four-seamers and curveballs have gone over his career. This is borrowing information from Brooks Baseball, and now this is expressed in terms of relative pitch height, where 0 corresponds to the vertical middle of the strike zone.

We can combine those lines into one. Here’s a rolling-average plot of the separation between Fiers’ average four-seamer and his average curve:

Fiers is around a career high for separation. Now, this isn’t necessarily all that well understood. We can’t look at this plot and automatically figure that Fiers has reached the next level. Some pitchers are successful with very little vertical separation. But it’s worth keeping in mind another fact. Looking at pitch movements for everyone who throws both a four-seam fastball and a curveball, only Hunter Wood and Daniel Mengden have a greater gap in vertical movement than Mike Fiers does. Fiers’ curveball drops almost two feet more than his fastball. That means that, if Fiers wants to throw a curveball that doesn’t spike in the dirt, he has to throw it up. Some visualization will help this, so, for the last picture, I’ll borrow from Texas Leaguers:

Those are side views of Fiers’ pitches before and after the trade. What I think is important is the curveball line, relative to the four-seamer (FF) line. Before the trade, Fiers’ curveball had a much more prominent hump, compared to the heater. In theory, that would’ve made it easier for the hitter to identify. More recently, Fiers’ curveball has looked more like his other pitches out of his hand. His four-seamer has been higher and his curveball has been lower, such that, when the hitter is around the decision point, the pitches are that much tougher to distinguish. This is just a way to talk about tunneling.

To be clear again, I can’t just draw a straight line from these adjustments to Fiers’ success. He also throws other pitches, and everything in a repertoire is supposed to work together. Fiers might well be on the verge of a slump, for all I know, and maybe he’s about to get back into home-run trouble. We still can’t conclude that the A’s would or should feel comfortable starting Fiers in a potential postseason game. What’s significant is that, a few weeks later, Fiers’ stock has improved. The A’s have given Fiers a pitch plan, and the early results have been terrific. Fiers has already helped in 2018, and he’s under club control for 2019, too. This looked like it was an unremarkable trade, but sometimes teams can get new value out of familiar players. It’s enough to make you want to believe in just about everyone.