The MVPs of the Yanks-Red Sox rivalry

We were looking this week for a discussion topic that would stir up both Yankees and Red Sox fans, as the two teams prepare to clash this week. We think we found one.

In this current iteration of the Yankees-Red Sox rivalry, which started when both teams made the postseason in 1995 (something that wasn't possible before the wild card was instituted), which hitters and pitchers have played the biggest roles in their teams' regular-season performance against each other?

Simply put, who has been more important: Manny Ramirez or Derek Jeter? Alex Rodriguez or David Ortiz? Pedro Martinez or Mariano Rivera?

Feel free to discuss, cajole and argue, in whatever manner you wish. But our plan is to offer a statistical take on the subject.

For that, we used a tool known as win probability added (WPA), a stat devised by sabermetric whiz Tom Tango and tracked historically via the box scores provided on Baseball-Reference.com.

WPA provides a statistical answer to the question: Whose pitching or hitting contributions were most important to their team's chance to win?

A player accumulates WPA based on situational performance. For example:

On June 3, 2007, A-Rod came to bat against Red Sox closer Jonathan Papelbon in the top of the ninth inning with two men out, no one on base, and the two teams tied.

Baseball historians have charted games to determine that in that specific instance -- tie game, top of the ninth, two outs, nobody on -- the visiting team wins 38 percent of the time.

In the confrontation between the teams' two stars, Rodriguez won. He hit a dramatic go-ahead home run.

Now, a new situation: The visiting team (Yankees) is ahead by one, with two outs and nobody on in the top of the ninth. In that instance, the visiting team wins 78 percent of the time.

So Rodriguez gets a credit of 40 percentage points (0.40) to account for his home run. Papelbon gets a debit of 40 percentage points (minus-0.40) to account for allowing the home run. The 40 comes from looking at how much the Yankees' chance to win increased (from 38 to 78 percent) after that plate appearance.

Take all of a player's credits and debits for every plate appearance in the rivalry, and you get a number that tells you how many wins that player's performance was "worth" to his team.

The beauty of WPA is that it separates the ninth-inning go-ahead hits from the home runs in 10-0 blowouts.

If you want to take the mathematics out of it, think of it this way: WPA will tell us whose hitting and pitching performances in the Yankees-Red Sox rivalry have been most meaningful.

Before we take a closer look, we should mention that we established some ground rules. This is a regular-season evaluation. The postseason is its own animal, and to compare the regular season to the postseason, or to mix the two in some manner, does a disservice to postseason play. And we're looking at only two elements of the game -- hitting and pitching. Baserunning, defense and "intangible contributions" are non-factors.

As far as the games go, everything counts. A Yankees-Red Sox game in April is as important as a game in September. Fair or unfair, our system is such that every game carries the same weight. The Yankees want to beat the Red Sox every time, and vice versa. So it all means something.

Let's look at the results:

• The most valuable Red Sox hitter in the Yankees-Red Sox rivalry is: MANNY RAMIREZ.

Intuitively speaking, if you've followed the rivalry, this makes sense. In fact, it's not even close. Ramirez's WPA is 5.906, better than double that of the nearest Red Sox player. In 112 games in the Yankees-Red Sox rivalry, Ramirez hit .340 with 33 home runs and 90 RBIs. The key to those numbers is how many of those home runs were meaningful. Of the 33 home runs, 28 of them (85 percent) came in situations in which the game's margin at the time was within three runs, one way or the other.

Next up on the Red Sox list is Kevin Youkilis, whose .450 on-base percentage and .944 OPS against the Yankees have made him a bugaboo of the highest level. Want to rack up WPA points? Do what Youkilis has done with runners in scoring position against the Yankees -- a .338 batting average, .481 on-base percentage and .584 slugging percentage. Those include a lot of meaningful moments.

The ranking most likely to generate discussion among Red Sox fans is Nomar Garciaparra's. He's third among the Red Sox hitters, edging out Ortiz.

• The most valuable Yankees hitter in the Yankees-Red Sox rivalry is: ALEX RODRIGUEZ.

I polled four Yankees fans I know, asking them who the top Yankee would be in this system. I expected all four would guess Derek Jeter, Bernie Williams or Jorge Posada. Much to my surprise, three guessed the person who finished second to A-Rod: Paul O'Neill. When I told them how O'Neill scored significantly higher than the likes of Jeter, Williams and Posada, the response was unanimous:

This system is pretty smart.

Rodriguez wins out, based partly on the strength of hitting three late-inning, game-winning home runs against Boston (versus Curt Schilling, Papelbon and Junichi Tazawa in the 15th inning last season). But O'Neill is the better story here.

From 1995 to 2001, few players on any team tormented opposing pitchers as O'Neill tormented the Red Sox. His 16 home runs don't seem overly impressive, but a dozen of them came with the score tied or the Yankees up/down by one run. Wanna talk clutch? This is clutch:

On May 4, 1995, O'Neill came up against Red Sox lefty Derek Lilliquist, with the Yankees down a run in the eighth inning. He homered to tie the game. Two batters later, Don Mattingly homered, and the Yankees went on to win 5-3.

On June 20, 2000, O'Neill homered in the eighth inning against Pedro Martinez, extending a 2-0 lead to 3-0. That provided some much-needed support. The Red Sox put one runner on base in each of the eighth and ninth innings but never got the tying run to the plate, as the Yankees held on for a 3-0 win.

On April 22, 2001, the Yankees trailed the Red Sox 3-2 in the bottom of the 10th. With one out, O'Neill homered to tie the game off Boston closer Derek Lowe. Two batters later, David Justice homered to win the game.

I think we can all agree that any at-bat in the following situation is vital:

• Seventh inning or later
• Score tied, or a one-run game

From 1995 to 2001, O'Neill had 50 plate appearances against the Red Sox in those situations, which equates to about seven per season. He hit a ridiculous .415 with three home runs, 13 RBIs, nine walks and a gargantuan .520 on-base percentage. It's hard to find someone more clutch than that.

Some of you may want to know about Posada's presence, since his rep for big moments against Boston is pretty good. (Said one Red Sox fan polled: "He's the one guy I fear most in a big spot.") Posada ranks a respectable third in Yankees value, with his bat worth 1.308 wins -- though if you narrow your focus to "since 2003," his performance approaches O'Neill's level and is tops among Yankees.

Where's Jeter on this list? Remember, we told you -- everything counts. Every at-bat. Jeter has a .293 batting average and a .768 OPS in his career against the Red Sox, not quite to the level of his peers.

There have been a lot of times when Jeter came through in big spots. But there have been enough times when he didn't to knock his WPA down a peg. Remember, fielding is out of the mix, so famous tumble-into-the-stands catches don't earn him any bonus points. He rates as the 13th most valuable Yankees hitter against the Red Sox since 1995.

• The most valuable pitcher in the Yankees-Red Sox rivalry is: MARIANO RIVERA.

How can this be, many Red Sox fans will say, when Rivera has blown so many saves against us?

Well, WPA is about the accumulation of big-moment performances, and Rivera has plenty of them. Forty-nine saves over 16 seasons helps accumulate WPA points. The quantity is impressive, and makes up for his 12 blown saves and six defeats.

The difference between Rivera and Pedro Martinez is 0.1 of a WPA point. So if a Red Sox fan wants to take Martinez in this argument, you can't argue much.

Of course, the Yankees fan has a bone to pick here. The Yankees, after all, were Martinez's "Daddy." He was 9-10 against them in 27 appearances. But there were a lot of good starts in there. (Remember the 17-strikeout one-hitter in 1999, the four-hit gem in 2000, and the three no-decisions Martinez had in 2001 in which the Red Sox lost by one run?) A few bad outings couldn't hurt his score enough to knock him down the list.

The Yankees fan has an alternative to Rivera in Andy Pettitte, whose numbers check in at 18-9 with a 3.68 ERA in this rivalry. His WPA checks in about half a point below Rivera's and Martinez's, but there's no one else anywhere near him in our standings.

Look at the two lists of most valuable pitchers, and there's one huge surprise near the top. What the heck is Frank Castillo doing there? Let's explain:

Castillo was 16-24 with a 4.66 ERA for the Red Sox, mostly in the doldrums that were 2001 and 2002. He did one thing well, though. Castillo made five starts against the Yankees. Three of them were really good, and in the two that weren't, he pitched well enough to keep the Red Sox in the game (a key to not getting hurt by negative WPA).

Castillo also had a pretty impressive relief stint mixed in there, one in which he not only pitched shutout ball, but the Red Sox also went from trailing to leading with him in the game. That helped his WPA, and he did nothing else within his brief stint to significantly damage it.

• The most valuable play in the Yankees-Red Sox regular-season rivalry is: BILL MUELLER'S WALK-OFF HOMER IN 2004.

Yankees and Red Sox fans probably don't need a stat to confirm this, as they remember the significance of the game on July 24, 2004. That was the day Jason Varitek and A-Rod brawled, and the Red Sox completed a comeback from a 9-4 deficit when Mueller hit a two-run walk-off home run against Rivera.

Statistically, the Red Sox win probability jumped from 24 percent before Mueller's home run to 100 percent afterward, but the lasting impact of that day went far beyond statistical value for a Red Sox team that found the Yankees to no longer be invincible.

The top three Red Sox moments in the rivalry by win probability jump, since 1995:

1. Mueller's home run

2. Ramirez's walk-off two-run single against Rivera with two outs in the 10th inning, giving Boston a come-from-behind 3-2 victory on April 13, 2001.

3. Garciaparra's game-tying triple in the ninth inning against Rivera on June 1, 1997. The Red Sox's chances for victory jumped 61 percent, but the Yankees reversed that when Rivera escaped a messy jam, and the Yankees went on to win in 15 innings.

The top three Yankees moments by win probability jump, since 1995:

1. Bernie Williams' game-tying single off Ugueth Urbina in the bottom of the ninth on July 21, 2002, which increased the Yankees' victory chances from 35 percent to 94 percent, particularly when Williams was able to advance all the way to third base on Trot Nixon's error. Three walks (two intentional) later, and the Yankees had a win.

2. John Flaherty's game-winning hit and Jeter's chin-splitting leap into the stands catch get all the attention, but the play from the Yankees' epic 5-4 win on July 1, 2004, that changed the game most was Miguel Cairo's game-tying double, before Flaherty's heroics. It raised the Yankees' win probability by 51 percent.

3. O'Neill's previously mentioned 10th-inning game-tying home run, and Justice's game-winning home run off Derek Lowe on April 22, 2001. Both had virtually identical contributions, in terms of their impacts on that contest.

• The least valuable player in the Yankees-Red Sox rivalry is: DEREK LOWE.

It seems appropriate, since we spent most of this space listing the most valuable players, that we answer the question of who was the least valuable. One pitcher stood out far beyond anyone else in the rivalry.

Lowe got beaten up by the Yankees quite a bit, both as a reliever and as a starter. In the first two seasons Lowe faced them, he allowed 14 runs in 9 1/3 innings. In 2001, out of the bullpen, Lowe blew two saves and had an 8.59 ERA against the Yankees.

And then there's the 2004 regular season. That year, Lowe made five starts against the Yankees, and three of them fall into the category of abysmal (23 runs allowed in 8 2/3 innings). Take those three games, add them to some of Lowe's other disasters, and you get a WPA score of minus-2.441, far worse than the next player (Varitek, minus-1.77). Jose Contreras is the worst-rated Yankee, at minus-1.572 wins.

Of course, Red Sox fans will tell you that they'll take Lowe's WPA, so long as they can also keep Lowe's win in Yankee Stadium, starting on two days' rest, in Game 7 of the 2004 ALCS. Did that make Lowe one of the most valuable performers of the Red Sox-Yankees postseason rivalry?

Sounds like a discussion worth having another time -- maybe in October.

Mark Simon is a researcher for "Baseball Tonight" and a frequent contributor to ESPNNewYork.com's Mets blog.