As you might expect, this is largely a modern phenomenon, made much more doable by the explosion of home runs in the mid-1990s. Indeed, a qualifying starting pitcher had allowed more home runs than walks just three times in all of history prior to 1998 (Tommy Bond in 1874, Robin Roberts in 1956, Gary Nolan in 1976), then happened three times in 1998, and it's happened 13 more times since. A bit like a hitter's 50-homer season, it's still very rare, just a lot less rare than it once was.
It's also, though, largely a Twins thing, and specifically a last-decade Twins thing. In the decade running from 2000 through 2009, pitchers accomplished the feat (if that's what it is) 10 times. The Twins had three different pitchers do it, a total of five times, all between 2002 and 2006. No other team has seen more than two pitcher seasons like this in its entire history; the Twins had five in five seasons.
I don't know if that's a point of pride, necessarily, but it's a reminder that "pitch to contact" really used to be a thing, and a thing that worked. Former pitching coach Rick Anderson's whole philosophy was to pound the strike zone and limit walks. It was an against-the-grain tactic that required exactly the right kind of pitcher to work, and in the mid-00s, the Twins were able to develop or acquire a large number of exactly the right kind of pitcher. "Pitch to contact" got to be kind of a joke a few years ago, as it appeared to many of us that Anderson was trying to force a number of square pegs through that round hole -- particularly Francisco Liriano, whose many talents did not include pounding the strike zone or regularly inducing soft contact. It's also possible that strikeouts have become such a vital part of every pitcher's game in just the past few years that this would no longer be a viable strategy with any sort of pitching staff.
In the middle of last decade, though, with the three guys below, and to a lesser degree the likes of Joe Mays, Kyle Lohse and Kenny Rogers, they had just the sorts of talents they needed to make it work, and that was a big part of their success--behind Johan Santana, of course, for whom I imagine the coaching strategy exclusively involved saying "you go do your thing, Johan" once every five days or so.
Here's the full list of the 14 pitchers who have allowed more homers than walks, in a total of 19 seasons (along with each of the three guys below, David Wells and Jon Lieber also did it twice). Here are the three Twins pitchers who've done it, in order of their first time doing it:
Rick Reed: we probably can't give Anderson too much credit (or blame) for this one, as Reed did it in 2002, Anderson's first year as pitching coach for the big club, and had also done it in 1998, with the Mets. Reed always had great control, but posted a league-best 1.2 BB/9 in 2002, walking 26 while allowing a career-high 32 homers. He managed a solid 3.78 ERA (118 ERA+) in 188 innings, thanks to that control and, probably, more than a bit of good luck.
Brad Radke: probably my all-time favorite Twin (I wrote a chapter on him in this e-book), and deservedly the poster boy for the Twins' pitch-to-contact reputation. One of the several things that made Radke (nearly) great was that after his nightmarish first two seasons, in both of which he led the league in homers allowed (and was a great sport about it, appearing in
Carlos Silva: you might remember Silva's 2005, in which he walked a ridiculous 9 batters in 188 innings, for an MLB record 0.43 walks per nine innings. Not giving up more home runs than walks under those circumstances would've been pretty astounding, but he gave up an average-ish 25, and posted a nice 3.44 ERA (130 ERA+) in 188 1/3 innings. He did it again in 2006, perfectly illustrating how this particular achievement is neither a good nor a bad thing: everything got worse from 2005 to 2006, and Silva gave up a league-high 38 home runs (interestingly, five of the 19 seasons on the list led the league in home runs allowed, but Silva is the only Twin to have done so) against a far more human 32 walks, and put up a 5.94 ERA (75 ERA+) in 180 1/3 innings. He'd have a nice bounceback-to-the-middle season in 2007, which convinced the Bill Bavasi-led Mariners to sign him to a bafflingly huge contract, under which he'd throw a total of 183 2/3 innings in two years, with a 6.81 ERA (62 ERA+).
I don't know what any of this means, or that it means anything, but the fact that the Twins did something five times in five years that's only been done 19 times by anyone ever is really interesting to me. I don't think Anderson's pitch-to-contact approach is workable these days, with the league strikeouts per 9 innings hovering near 8 and only two pitchers in the MLB top 10 in WAR posting K/9s under 8 (and most of them well over a strikeout an inning). Strikeouts are to a large extent driving the league (and especially pitching) right now, they're a thing you just have to have to be successful (as a pitcher or as a team), which is something the team's current administration appears to understand at least a bit better than the last one did. But 2002-06 was a different time, where league-wide strikeouts were down about 1.5 from today, and the Twins appear to have found an undervalued set of skills in pitchers--a set that helped make them division champions four times in those five years.
Mostly, though, I think handing out more homers than walks over the course of a full season is just a fun, quirky thing, and it'll be fun to see if Hughes finally joins their ranks this season.