Somehow, I’ve missed Matt Duffy being a rookie this year. Even after perusing the Fangraphs rookie leaderboards and the MLB.com rookie stats pages I missed his name…every…single…time. I don’t get it. So let’s fix that.

Duffy currently ranks third among rookie hitters in WAR, trailing Kris Bryant and Joc Pederson – the usual suspects. When you think of Bryant and Pederson you think of crazy power, but what’s nuts is Duffy’s .460 slugging percentage is only six points less than Pederson’s…and five points higher than Bryant’s. On a park-neutral basis (wRC+) Duffy (127) has performed almost as well as the two sluggers (Pederson 133, Bryant 129).

Duffy hit 13 home runs in 1,087 minor-league plate appearances over three seasons. In his 2014 MLB debut Duffy hit zero homers in 64 PAs. This season he’s hit eight homers, bringing his Isolated Power to .163 – 54 points higher than his minor-league ISO mark. Duffy benefited from a great June, where he slashed .313/.359/.594 with six doubles, three triples and five home runs. His home run totals in April, May and July, respectively, are one, two and zero. His Iso marks by month, in order: .109, .113, .281, .090.

Duffy’s June stands out well above the other months, so let’s explore why. In Duffy’s homerless 2014 he had a 26 percent fly ball rate, and that number has actually decreased to 25 percent this year. His line drives have actually decreased from 32 percent last year to 21 percent this year, while his ground ball rate has risen dramatically, up from 41 percent in ’14 to 53 percent this year.

He does have a pretty sustainable 13 percent home run per fly ball rate on the season, and even in June he had a 17 percent HR/FB rate. But that’s because his fly ball rate in June ballooned to 36 percent, 14 percentage points higher than any other month this season. His ground ball rate cratered to 45 percent, which is 10 percentage points lower than any other month. So, in short, he hit more home runs at a reasonable rate because he was hitting more fly balls. But he’s reverted to fewer fly balls in July, following the same path as April and May.

It does seem like Duffy’s June was an outlier. In fact, take a look at Duffy’s home runs and you’ll see he has benefited from some lucky shots. Two of his home runs have only cleared the fence at AT&T Park in San Francisco by the first row/walkway and two road home runs – one in Milwaukee and one in Philadelphia – hit so close to the field they actually bounced back onto the playing surface.

Duffy’s been vital to the Giants this season and to many fantasy teams who had the foresight to pick him up. While his minor league stats (.304/.387/.413 with high BABIPs, good K and BB rates and high steal totals) say he can be a productive major leaguer, I wouldn’t count on him continuing his June power run unless he changes his approach.