Is he good enough to be a left-handed spot reliever in the majors?

Certainly. That’s one of the least demanding roles in the majors. Rapada is a left-handed sidearmer, which is the typical profile. He hasn’t pitched very well — a career 89 ERA+ — but he’s pitched to more than 40 batters in only two seasons. Of those, one has been a good season and one not-so-good. That, too, fits the profile.

He’ll get his chance to make the majors with the Yankees, who signed him in February after the Orioles released him.

In 2011, Rapada pitched in 32 games for the Orioles, and 16 1/3 innings. Is this the extreme of specialization?

The theoretical limit is that a pitcher can pitch to one batter per appearance. In Rapada’s 32 games, he faced 69 batters; or 2.16 batters per appearance. However, in 2011, Randy Choate of the Marlins ”broke” the 2 batters per appearance barrier. with 103 batters faced in 54 appearances (1.96 per appearance.)

I can conceive of a veteran left-handed spot pitcher who is completely ineffective against right-handers getting into something like 80 games, facing perhaps as few as 100 batters.

Most sophisticated analysts have concluded that reserving a roster spot for someone so specialized as this is a bad idea. Is it?

First, aesthetically, I think the constant in-game platoon matchups, and the use of one-inning-at-most relievers, is bad for baseball. It slows the game down and makes it less exciting. It’s why I think baseball would have been better off if Tony LaRussa had never managed.

But, I’m not sure that reserving a roster spot for a lefty spot reliever is necessarily a bad idea. I’m not sure how much the typical 25th man plays. It only makes sense to compare the value of a left-handed spot reliever to that of the least-valuable position player. The position player can be used as a pinch hitter, pinch runner, or defensive replacement. His value as a pinch runner is negligible. It’s certainly possible that the last man on the bench would not be playing in as many as 120 plate appearances — either on offense or defense. When you factor in the likelihood that your left-handed spot reliever will be used in more critical situations, it’s possible — not certain — that the lefty reliever is more valuable.