Joe Girardi has a reputation as a smart, stats-savvy manager. But, with his recent usage of Mariano Rivera, he appears to be unfamiliar with the concept of leverage.

For those of you who are not so sabermetrically inclined, “leverage” is the idea that when it’s a really important part of the game with, like, the score being close in later innings late – you should use your best available pitcher. To the contrary, when the game is not so much on the line, you should not waste that pitcher because you might be forced to rest him in a subsequent situation with higher leverage. Follow?

Fangraphs features a play-by-play Leverage Index which tells you how much the game is on the line. All games start off at a neutral 1.00. If the game remains close into the late innings, the Leverage Index goes up above 1.00. If the game becomes a blowout, the Leverage Index falls below 1.00. It updates this live throughout a game. Somebody get Joe a laptop!

Example: In Oakland on Tuesday night, the Yankees had a 4-run lead going into the bottom of the 9th. At this point, you can throw pretty much anybody out there against the jokers in the A’s lineup. A league-average pitcher will secure the win here 99% of the time. Now, the choice of Damaso Marte makes less sense than others, since he’s a lefty and the first two guys due up are righties…but whatevs. Maybe Joe had a gut feeling. So, Marte does the worst possible thing and walks the first batter (apparently Marte’s 6.35 BB/9 against RHBs isn’t in Joe’s stats binder). Girardi calls for Rivera.

The leverage of that situation was .97… below average. There’s no need to waste Mo in that situation. Bringing in DRob or Ace or even Mitre still keeps your win expectancy at about 98%. Using Mo to squeeze out an extra percent or so of win expectancy is not efficient.

Fast forward one night to Game 2 of the Oakland series…8th inning, Yanks up 2-0 on a gem of a game by Phil Hughes. After Chavez’ comebacker breaks up the no-no, Hughes K’s Kouzmanoff, but walks Gross. Now with two on and one out, the leverage is 4.12. Girardi decides to go to pen and calls for… Joba Chamberlain. We all agree Joba is an above-average pitcher, and we hope he can regain his old form at some point. But whatever he is, he’s not The Best Relief Pitcher In The History Of Mankind. That title belongs to a man who was resting his Panamanian rump on the bench when leverage was over four times the neutral game situation.

After Joba gets Adam Rosales on a flyball to right, Jake Fox fists one to opposite field for a run scoring single. It’s now 2-1, with runners at the corner and four outs to go. The Leverage Index is up to 5.12! The Yankees win expectancy has fallen to 69%. Can you think of a better spot to use your far-and-away, no-doubt-about-it bestest reliever? Mais non – Joe sticks with Question Mark and The Mysterians for another crucial out, which fortunately they get with a nice stab by Teixeira on a hard chopper to first.

Mo finally made it into the game… after the Yankees scored in the top of the 9th and the Leverage Index had dropped to 1.89.

For a supposedly-forward thinking manager, he doesn’t know how to maximize the impact of our Lord and Savior. We think Girardi is an above-average MLB manager (not exactly a great selection pool), but you cannot eschew higher leverage situations for lower ones with Mariano Rivera.