Adrian Gonzalezphoto © 2011 Keith Allison | more info (via: Wylio)

They say you shouldn’t sweat the small stuff, but in baseball, the small stuff is what it’s all about.

Sometimes, it’s all about big plays in big moments. Everyone likes a highlight reel home run or a diving stop at the hot corner. But no matter what appears on ESPN or the local news, baseball is always won or lost in high-leverage situations.

Sunday’s game against the Minnesota Twins was about as fun of a game as we have had considering how it started. We didn’t need a Mother’s Day miracle starring Julio Lugo. All we needed was an Adrian Gonzalez and his spot atop today’s leverage index.

If you are unfamiliar with the leverage index on FanGraphs, you should mosey on over and TAKE A LOOK. The leverage index is defined as “a measure of how important a particular situation is in a baseball game depending on the inning, score, outs, and number of players on base, created by Tom Tango.”

You can basically look at any situation that occurs in the game and see how it stacks up in terms of importance and affect relative to the game at hand.

In 2006, Tom Tango had this to say about leverage index:

It is a very simple concept—what is the chance of winning the game given a certain set of variables? At a minimum, the variables include the inning, score, base, and out. At a maximum, you’d include everything under the sun, such as the identities of the players, the park, the climate, the count, tendencies of managers, and a host of whatever you can think of. Like fan interference. Or managers’ insistence of sticking with a tired pitcher. Or pyschological trauma.

Almost four years ago, I introduced a concept called Leverage Index. Leverage is the swing in the possible change in win probability. If there is a game with one team leading by ten runs, the possible changes in win probability, whether the event is a home run or a double play, will be very close to negligible. That is, there won’t be much swing in any direction.

But, in a late and close game, the change in win probability among the various events will have rather wild swings. With a runner on first, two outs, down by one, and in the bottom of the ninth, the game can hinge on one swing of the bat—a home run and an out will both end the game, but with vastly different outcomes for the teams involved.

You can spot a high-leverage situation, I can spot them, and pretty much everyone can spot many high-leverage situations. All that’s left for us to do is to quantify every single game state into a number. That number is the Leverage Index.

So let’s look at LI relative to Sunday’s game at Fenway Park.

Gonzalez’ 3rd-inning, groundball single that scored Jacoby Ellsbury and tied the game at 3-3, rates the highest on the leverage index at 2.29. Anything over a 2.00 is critical on the scale. That single also carried with it, a win expectancy of 62.7%. It was a critical point in the game and helped swing the control in Boston’s favor.

You can look at Gonzo’s solo homerun in the 5th inning as as being critical as well (0.66 LI), but it was not nearly as big as Kevin Youkilis‘ fielder’s choice (1.92 LI) that scored Dustin Pedroia. An innocuous play at first blush, given that it was a FC, but it was nearly a “2” on the leverage index. When Youk scored on JD Drew’s base hit to left in that same inning (1.64 LI), it gave the Sox a 75% win expectancy.

All of Minnesota’s leverage seemed to happen early withJason Kubel starting the scoring in the first inning by plating Denard Span on a base hit (1.85 LI), as well as Danny Velencia’s two-run single (1.73 LI) that pushed the score to 3-0.

Daisuke Matsuzaka struggled early in Sunday’s game against the Twins but came up pretty big when they needed him to in the 5th inning.

After walking Denard Span to start the inning, the leverage index crept up to 2.00 again. Matsuzaka was able to get Trevor Plouffe to fly out to left (2.00 LI) and capture an out without allowing the speedy Span to advance a base while the Red Sox hung on to a 5-4 lead. It was a very important situation in the game — no matter which team the outcome favored.

The next batter was Justin Morneau and Matsuzaka made quick work of the big Canadian (1.66 LI) and again scored another win on the leverage index.

To close out the crucial 5th, Matsuzaka needed to play a game of cat and mouse with both Span at first base and Kubel at the plate. The Twins were looking to put some pressure on the Sox by either setting up a hit and run (maybe scoring Span from first if Kubel could good wood on the ball) or looking for a straight-out steal.

Either way, Matsuzaka threw over to first a five separate times, including four in a row, to keep Span in check. He was then able to get ahead of Kubel 0-2 before inducing a groundball out to end the 5th inning.

Kudos to Dice-K for battling back.

And although Jed Lowrie‘s two-run double in the 7th inning that made it 9-4 scored low on the leverage index (0.47 LI), it was the proverbial nail in the coffin for the Twins as it held a win expectancy of 98.2%.

No miracles needed in today’s Mother’s Day game at Fenway Park. It just required some big plays in some critical moments by Matsuzaka, Gonzalez and Youkilis.

Leverage Index is a fun way to see the game through a slightly different lense. Often times, small subtle plays (like the Plouffe out) are bigger than you realize.

Now let’s get up and over .500 and stay there.