Trevor May's improved walk rate may not be here to stay

Usually, a player's results in the minor leagues will portend his performance in the majors. Those who set the farm on fire will usually do the same at the show, while those who struggle to keep up in the lower levels won't fare any better in the highest one. The former axiom has some exceptions — just ask Brandon Wood — but the latter almost always applies. The greater quality of talent in MLB means that mediocre players will usually resemble their prospect selves. In other words, they'll be who we thought they were.

Trevor May, in 2015, wasn't who we thought he'd be. As a 25-year-old rookie, he put together a splendid campaign: His 80 FIP- was on par with Madison Bumgarner, and his cFIP of 83 matched up with Noah Syndergaard. Although those figures came across 114.2 innings, which doesn't make for a particularly large sample, they nevertheless look encouraging. Since the Twins have a pretty shallow rotation, they would welcome a repeat performance from May in 2016. For him to accomplish that, he'll have to sustain a truly incredible improvement.

Last season, May excelled in the three most important areas of pitching: strikeouts, walks, and home runs. His rates of each (22.4 percent, 5.3 percent, and 2.2 percent) were significantly better than MLB averages. We might have seen the punchouts coming, since he did it 27.2 percent of the time as a minor leaguer. Likewise, he preceded his MLB home run avoidance with similar success in the minors, where 1.8 percent of opponents hit the ball out of the park. Those free passes, on the other hand...well, take a look at this:

These are May's career results in the minor leagues, from Single- to Triple-A. If you squint hard enough, you can maybe see a trend in the right direction, but you can't dispute the overall point: As a farmhand, May had a lot of trouble with free passes. Over 775.0 innings, he walked 11.6 percent of the batters he faced — more than twice his mark from 2015. Can he maintain that unbelievable progress?

On a basic level, May deserved the production. Last year, he threw 66.4 percent of his pitches for strikes, per Baseball-Reference, which topped the MLB average by more than two percentage points. Along with a solid rate of in-play strikes — which helped him keep plate appearances short — and the aforementioned strikeout rate, that gave him a 5.9 percent expected walk rate. So he didn't fluke his way into this production, in theory.

May's plate discipline metrics yield another encouraging development. As we all know, a pitcher can avoid walks two ways: by pounding the zone or getting hitters to chase. May didn't have a great O-Swing rate in 2015, at 30.9 percent, but his zone rate of 51.8 percent stood out. Out of 141 pitchers with at least 100 innings, only 15 threw the ball over the plate more frequently than that. Pitchers control zone rate more than they do O-Swing rate, which could give May a better chance of preserving his low walk rate.

This change didn't start in 2015, either. May's major-league debut came in August of 2014 as a late-season call-up for a terrible Twins team. Working 45.2 innings across 10 appearances, he compiled a subpar 10.3 percent walk rate, around what we might predict based on his resume. However, most of that damage came in his first three games, when he walked an amazing 26.5 percent of opponents. In outings 4 through 10, his walk rate plummeted to 5.5 percent. The following February, May spoke to MLB.com's Rhett Bollinger about the latter stretch:

May's ERA in his 10 appearances, including nine starts, was 7.88, but he struck out 44 in 45 2/3 innings and started to cut down his walk rate. After walking 13 in his first nine innings, May walked just nine in 36 2/3 innings the rest of the way.

He credited former Twins pitching coach Rick Anderson for tweaking his mechanics, and said he's worked hard this offseason to stay taller in his drop-and-drive delivery.

"Toward the end, I stayed taller and my stuff got better," May said. "I got more swings and misses. The runs that were scoring were more in spurts. And the walks got better, too. I started pounding the zone better than I ever have."

Not only did May's results change, he seems to have adjusted his approach to effect that change. Perhaps the 2015 Trevor May will be here to stay.

Then again, we can't really ignore his past. Most of the time, a pitcher's control won't get better as he advances to the major leagues. To prove this, let's look at an informal comparison. Using Chris St. John's JAVIER prospect comparison system, I isolated pitchers with at least 400 career minor-league innings and a walk rate z-score between 0.3 and 0.6 (May's z-score was 0.48). This meant the pitchers had sizable track records of high walk rates, and for the most part that translated to the show:

This 22-man group had a weighted average minor-league walk rate of 10.9 percent. The mere nine who made it to the majors averaged a 9.5 percent walk rate there. In other words, they clearly kept struggling with bases on balls — which really sets May apart, and not necessarily in a good way.

Plus, his new strategy has some drawbacks. When evaluating pitchers, we must note the distinction between control and command — control means a hurler throws the ball over the plate, whereas command means he can stay out of the middle of it. May's zone plot from 2015 illustrates his shortcomings with the latter:

Unsurprisingly, May posted an unsightly .340 BABIP last season, backed up by a subpar hard-hit rate of 29.8 percent. His approach shouldn't bear all the blame for that — his defense didn't do him any favors, and he had a minor-league BABIP of .312, so that wasn't too out of the ordinary. Still, he probably wouldn't have allowed so many hits without pounding the zone.

Interestingly enough, both ZiPS and Steamer think May will keep this up in 2016: The former projects a 7.9 percent walk rate, the latter a 7.0 percent walk rate. Based on his achievements in the past and the shaky nature of his 2015 production, I can't say that I share their optimism. May might have some legitimate changes behind his rise, but I'll need to see more before I can buy into it.

All fans of baseball, even the fun-hating sabermetric ones, love a breakout story. Players who come out of nowhere to prosper at the highest level in the world light up our day. These stories don't happen often, though, and for every player who actually makes the leap, many more will stumble in their quest for greatness. This isn't to say May will perform horribly this season, but rather to caution against reading too deeply into a one-year sample. Those walk issues have always defined him, and I wouldn't expect that to stop any time soon.

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Ryan Romano is an editor for Beyond the Box Score. He also writes about the Orioles on Camden Depot (and on Camden Chat that one time) and about the Brewers on BP Milwaukee.