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Diamondbacks starters can't go deep: is it a problem?

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We look at whether the assumption that the Diamondbacks starters can't go deep into games is true compared to the rest of the league, and then try to answer whether its really a problem.

Matt Kartozian-USA TODAY Sports

It's become something of a joke in the Gameday Threads about how Arizona's starting pitching seemingly can't go deep into games. It certainly seems like a problem, and an average of 5.017 IP/GS seems to be low. But are they really?

The second assumption can be answered fairly easily. Yes, the Diamondbacks have been one of the worst in getting lengthy starts from their pitchers. This table shows each team's innings pitched per game started as kind of a crude measure for the average length starters are lasting per team:

Team GS IP IP/GS
Tigers"]">Tigers 6 39.1 6.516666667
Athletics"]">Athletics 7 44.1 6.3
Nationals"]">Nationals 6 37.2 6.2
Royals"]">Royals 6 37.2 6.2
Reds"]">Reds 6 36.2 6.033333333
Cardinals"]">Cardinals 5 30.1 6.02
Dodgers"]">Dodgers 6 36.1 6.016666667
Astros"]">Astros 6 35.1 5.85
Angels"]">Angels 6 35.1 5.85
Mets"]">Mets 6 35 5.833333333
Red Sox"]">Red Sox 6 34.2 5.7
Pirates"]">Pirates 6 34.2 5.7
White Sox"]">White Sox 6 34.1 5.683333333
Rays"]">Rays 6 34 5.666666667
Padres"]">Padres 7 39.1 5.585714286
Mariners"]">Mariners 6 33.2 5.533333333
Brewers"]">Brewers 6 33.2 5.533333333
Braves"]">Braves 6 33.2 5.533333333
Rockies"]">Rockies 6 33.2 5.533333333
Phillies"]">Phillies 6 33.1 5.516666667
Giants"]">Giants 7 38 5.428571429
Cubs"]">Cubs 5 26.1 5.22
Blue Jays"]">Blue Jays 6 31.2 5.2
Indians"]">Indians 6 31.1 5.183333333
Yankees"]">Yankees 6 31.1 5.183333333
Twins"]">Twins 6 31.1 5.183333333
Marlins"]">Marlins 6 30.2 5.033333333
Diamondbacks 6 30.1 5.016666667
Rangers"]">Rangers 7 35.1 5.014285714
Orioles"]">Orioles 6 29.1 4.85
Average

5.603952381

The D-backs weren't much better last year over the full season:

Team GS IP IP/GS
Reds 162 1023.2 6.316049383
Braves 162 1014.1 6.259876543
Phillies 162 1013.1 6.253703704
Tigers 162 1007 6.216049383
Nationals 162 1002.1 6.185802469
Athletics 162 996 6.148148148
Brewers 162 992.1 6.124074074
Royals 162 986.2 6.087654321
Mets 162 985 6.080246914
Giants 162 977 6.030864198
Dodgers 162 975 6.018518519
Pirates 162 971 5.99382716
Red Sox 162 970.1 5.988271605
Astros 162 970 5.987654321
White Sox 162 970 5.987654321
Cardinals 162 969.1 5.982098765
Blue Jays 162 958.2 5.914814815
Indians 162 955 5.895061728
Rays 162 954.2 5.890123457
Orioles 162 953.2 5.883950617
Mariners 162 952 5.87654321
Yankees 162 951.2 5.871604938
Padres 162 951.1 5.870987654
Marlins 162 947.1 5.846296296
Angels 162 942.2 5.816049383
Diamondbacks 162 937.1 5.784567901
Cubs 162 927 5.722222222
Rangers 162 918.2 5.667901235
Twins 162 913.1 5.636419753
Rockies 162 905.1 5.587037037
Average 5.964135802

It's clearly not a figment of our imagination. Is it a problem, though? That's a little harder to figure out.

If we look at the last few years to see who has been making the playoffs, it does like most of the teams are in the top 10 for IP/GS: 5 of 10 in 2014; 7 of 10 in 2013; 5 of 10 in 2012; 5 of 8 in 2012, including the Diamondbacks. But if the difference between the 10th best team and the worst isn't dramatically different, instead only showing a gap of less than an inning. Between the top team and the bottom there's more variance, but it's usually only about an inning, and in 2014 was less than an inning.

Spread out over 162 games an inning every game will carry a larger difference, as you're calling on your bullpen earlier every night over potential rivals. But depending on how your bullpen is structured it might be easier to be managed because those extra innings might be absorbed with a good long reliever, or if you have a bullpen that is talented from the top to the bottom.

Of course, using the postseason as a result from starter longevity is problematic because it doesn't represent if the pitching is effective, only if the team played well. The Angels last year were the 6th worst team for getting long starts, yet their offense was so good that they ran away with their division. What if instead we compare IP/GS to starting pitching fWAR?

It seems there's some positive correlation, but not an overwhelming one:

2014ip-gs
2013ip-gs
2012ip-gs
2011ip-gs

This is only a handful of years, I didn't run any statistical tests beyond simple correlation. This isn't a finished study by any means, but it might serve as a starting point for some of the members of the community that are smarter than me.

Other things I'd like to consider would be a larger data set, comparing IP/GS to a rate stat instead of a counting stat (it makes sense that the longer a pitcher is out the more WAR they can accumulate, and if they're making it into the 7th inning on a consistent basis they probably aren't too terrible in this age of pitcher specialization). And with increased specialization for relievers and the decline of complete games, is this correlation losing any meaning? If I looked at older years would there be a stronger connection?

Obviously the above is closer to a pilot study than a fully fleshed out idea, but it does show you're not crazy for wondering if the Diamondbacks currently aren't very good at going deep into games. It seems to matter some, but how much is still up for debate.