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Yankees have plenty of reasons to worry about Hiroki Kuroda

At 39, the Yankees' other Japanese starter seems to finally be showing his age.

Mike DiNovo-USA TODAY Sports

Through ten starts this season that have mostly ranged between "eh" and "ugh" on the monosyllabic grunt scale, Hiroki Kuroda has managed to fly somewhat under the radar. That's a good thing in a way - he's not on the DL like three-fifths of the Yankees' Opening Day rotation, and the performance of Masahiro Tanaka has overshadowed him a lot. But at this time last year, Kuroda was standing out in his own right with some of the best pitching of his major league career, carrying a staff that was fighting to keep a non-existent offense afloat. That hasn't been the case in 2014. For a 39-year-old who's had quite a bit of mileage put on his right arm the past few seasons, a precipitous drop in effectiveness is not something to feel very good about.

Kuroda's struggles go back to early August of last season, when he seemed to hit a wall after a first half that had him on the outskirts of Cy Young Award debates. In the twenty games he's started since August 1, 2013, Kuroda has an ERA of 4.98 and a WHIP of 1.40. He's allowed 1.26 home runs per nine innings - well above his career mark of 0.90, and he's contributed just 6.05 innings per start, also down from his personal norm. While Kuroda's pitched to some bad luck - his .303 BABIP against this year is a career worst, as is his 62.7 percent left-on-base rate - there are plenty of other troubling signs suggesting that a return to form beginning this week in St. Louis might not be in the cards.

Kuroda's been worked in his career - a lot - and during his time as a Yankee that strain has only increased. Between Japanese baseball and the American majors, he's tossed 2,879.2 career innings. As he's aged, he's pitched more, not less. Kuroda eclipsed the 200-inning plateau three straight years from 2011 through 2013, though he'd achieved that just twice before in fifteen seasons. He's also been working harder to get hitters out. In 2013 and 2014, his pitches thrown per batter faced are 3.89 and 3.78 respectively, both above his career rate. Due to a continuous slide in fastball velocity - his heater has dropped to 90.9 mph this year from 92.0 as recently as 2011 - he has relied more on splitters and breaking balls, pitches that are typically more taxing on the arm. 24% of Kuroda's offerings this year have been splitters, up from 14.7% for his career, while just 48.9% have been fastballs, down from 55.6%.

Age and fatigue haven't only led to a loss of fastball speed for Kuroda. His stuff simply isn't as sharp or as deceptive as it once was and hitters are having an easier time recognizing his pitches. This season, they've chased just 31.4% of balls outside the strike zone and they've swung at 69.8% of pitches within it. Kuroda's groundball and fly ball rates of 47.7% and 33.3% are off from his career marks as well. While his strikeout and walk rates have remained solid, batters seem to be making better contact when they put the ball in play.

At 39, it's fair to call a lackluster stretch that's gone on for around two-thirds of a season a decline, but there isn't much the Yankees can do about it. Thanks to the injuries to CC Sabathia, Michael Pineda and Ivan Nova, Kuroda's importance to the rotation has only grown. 4.2-inning, 100-pitch outings like what we saw on Friday in Chicago aren't going to cut it, especially for a bullpen that's routinely tested by replacement pitchers going three of every five days. There's no shame in what Kuroda's going through - plenty of pitchers would love to be able to do even what he's doing now at his age - but the Yankees really can't afford for it to continue. They don't have the depth to replace what they've already lost, let alone to even think about ousting Kuroda or reducing his role if he continues to scuffle. If nothing else, his showing-of-age reiterates the fact that even with an offensively-challenged middle infield and questions emerging at right field and DH, starting pitching is the team's greatest need.