New York Yankees: An In-Depth Numbers Crunch of the Bullpen's Hidden Problem

By Nick Tom
Rick Osentoski-USA Today Sports

The New York Yankees are surprising everyone.

After losing Russell Martin and Nick Swisher to free agency and Mark Teixeira, Curtis Granderson, and Derek Jeter to injury, prominent media members and fans alike expected a drop-off; it only made sense.

Now, the Yanks sit at 18-12, two games behind the Boston Red Sox, and in second place in the AL East. They’re defying expectations  — even their Pythagorean record is 16-14 — and are doing it despite a few huge holes in their construction.

Most thought that if the Yankees were to win, it’d be their pitching staff that helped pull the anchor until their injured reinforcements returned as healthy ones. More specifically, they thought their bullpen, bolstered by Mariano Rivera and David Robertson, would deliver late-inning dominance and provide their supposedly weak offense with surmountable deficits.

In a way, they were right.

Mariano is Mariano again. He’s 11/11 in save opportunities, isn’t walking anyone, and is striking out eight guys per nine innings. He’s, well, he’s glorious. But that’s where the bullpen strength ends.

A statistic that gives a good idea of a bullpen’s effectiveness is its inherited score percentage — the percentage of runners on base when a reliever enters a game who eventually end up scoring. It’s far from a perfect stat (it’s a lot harder to keep a man on third from scoring when there are no outs than a guy from first when there are two, for example), but it gives an idea.

With the Yankees’ super-inflated rate, it gives a scary idea.

Despite a league average 31 percent inherited score percentage, according to Baseball-Reference, the Yankees’ bullpen is allowing 47 percent of their inherited runners to cross the plate. They’re coming into games and aren’t closing the door on opposing lineups. They aren’t, well, relieving.

You could reasonably attribute this to manager Joe Girardi’s inability to get a good read on his pitchers and possibly leaving his starters in games too long, but the whopping 16 percent implies that there’s definitely more than one reason for this gross problem.

Why else might it not be Girardi’s fault? Last year, the Yankees’ bullpen only allowed 22 percent of its inherited runners to score. They were 7 percent better than last year’s average of 29 percent, and did it all without Mariano.

Oh yeah, about the whole ‘runner on third with no outs is hard’ thing. Think it might be because the bullpen is facing tougher situations?

Well, according to Baseball-Reference’s average leverage index, or aLi, the 2013 Yanks bullpen is entering games in lower pressure situations than it was last year. If 1.0 is average pressure and the higher the number, the higher the pressure, the 2012 Yanks’ aLi was .999.

2013’s aLi? .952. The League average? 1.002. The bullpen isn’t at the same level it was last year.

The question is why? One might look at the bullpen’s increased usage. You might blame the starters’ inability to pitch deeper into games, or you might again blame Girardi’s rigid by-the-book mixing and matching. Aside from the toll it puts on those watching (oh, it’s a big toll), it puts a toll on the bullpen’s arms.

In 2012, the average Yankee reliever threw 15 pitches per appearance and averaged 2.7 outs per game.  Now, the average reliever is throwing 21 pitches per game and is, on average, getting 3.8 outs.

Conversely, the arms are being used less often off short rest. In 2012, Yankee relievers with zero days’ rest entered a game 117 times, almost double the rate they’re entering them now. Their current rate, extrapolated to 162 games, would end up in 59.4 similar appearances.

Of those 117 entrances, pitchers no longer with the team made 49. Were those guys more capable of performing on zero days’ rest than the current roster? Who knows. Will pitching on zero days’ rest affect Mariano as the year goes on, especially considering his age? Maybe.

You might attribute some of the lower leverage situations to relievers being used earlier in games and therefore starting innings (low leverage) more often, but a 25 percent increase from last year is disconcerting.

You can confidently expect the difference to decrease as inning totals increase and numbers naturally regress toward the mean, but by how much? How much will increased pitches-per-appearance affect relievers as their innings pile up?

I’m not sure, but when Ivan Nova pulls a “hey guys! I need a lot of help!”, he won’t be getting much. And their usage won’t help change that.

For further baseball analysis, follow Nick Tom on Twitter @NickTomFB

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