Remember when we started the Impact Index, and I said we’d be focusing on more than just numbers? That we’d be peering behind the statistics to tell the stories of the unsung heroes? The long roads traveled by the middle relievers and utility guys who get little press but sometimes do big things to help their team win?

Yeah, well, sometimes the numbers are the story.

Last Thursday, Kansas City Royals platoon catcher Brayan Pena hit a walk-off, pinch-hit single in the bottom of the ninth against Milwaukee Brewers closer John Axford. The Royals were down 3-2, with two outs, and runners on first and second. Pena looped a liner to left field, scoring the runner on second. The Brewers then misplayed the ball on the relay, allowing the winning run to score. It looked like this:

Pena’s hit now sits atop the Pinch Hit Win Probability Added leader board for this season.

You’ll recall that WPA measures how a player affects his team’s Win Expectancy on a play-by-play basis. Win Expectancy is the percent chance a team will win based on score, inning, outs, runners on base and the run environment. It is calculated using data from every baseball game for which play-by-play information is available. Leverage Index measures how important a particular situation is in a game, factoring in the inning, score, outs and number of players on base. The Leverage Index is highest in the later innings, with the score tied or close, and runners on base.

Through Sunday’s action, there have been 1,852 instances where a pinch hitter had a single plate appearance in a game. He may have stayed in to play defense following his plate appearance, but he only batted once in the game. Another 248 times, a pinch hitter had more than one plate appearance in game.

Of the 1,852 “single” pinch hit appearances so far this season, Brayan Pena’s resulted in the highest WPA. Here’s the Top 10 “single” pinch hits of the season as ranked by WPA.

Rk Player Date Tm Opp Rslt R H 2B 3B HR RBI BB WPA
1 Brayan Pena 2012-06-14 KCR MIL W 4-3 0 1 0 0 0 1 0 0.831
2 Brandon Allen 2012-04-26 TBR LAA W 4-3 1 1 0 0 1 2 0 0.805
3 Jarrod Saltalamacchia 2012-05-26 BOS TBR W 3-2 1 1 0 0 1 2 0 0.716
4 George Kottaras 2012-04-17 MIL LAD W 5-4 0 1 1 0 0 2 0 0.668
5 Scott Van Slyke 2012-05-20 LAD STL W 6-5 1 1 0 0 1 3 0 0.576
6 Bryan LaHair 2012-06-07 CHC MIL L 3-4 1 1 0 0 1 2 0 0.524
7 Mark Kotsay 2012-04-26 SDP WSN W 2-1 0 1 1 0 0 2 0 0.510
8 Adrian Beltre 2012-05-05 TEX CLE W 5-2 1 1 0 0 1 3 0 0.485
9 Chad Tracy 2012-04-07 WSN CHC W 7-4 0 1 0 0 0 2 0 0.454
10 Jordany Valdespin 2012-05-07 NYM PHI W 5-2 1 1 0 0 1 3 0 0.453
Provided by Baseball-Reference.com: View Play Index Tool Used
Generated 6/18/2012.

But Pena’s game-winning pinch hit last Thursday isn’t just the best this season, as measured by WPA. It’s also on the Top 10 Pinch Hits WPA leader board for “single” pinch hit plate appearances over the last ten seasons (2003-2012).

Rk Player Date Tm Opp Rslt R H 2B 3B HR RBI BB WPA
1 Donnie Murphy 2010-07-19 FLA COL W 9-8 1 1 0 0 1 2 0 0.902
2 Bill Hall 2004-04-27 MIL CIN W 9-8 1 1 0 0 1 2 0 0.899
3 B.J. Upton 2007-09-08 TBD TOR W 5-4 1 1 0 0 1 2 0 0.896
4 Jason Giambi 2008-06-05 NYY TOR W 9-8 1 1 0 0 1 2 0 0.895
5 Brayan Pena 2012-06-14 KCR MIL W 4-3 0 1 0 0 0 1 0 0.831
6 Rajai Davis 2009-08-03 OAK TEX W 3-2 0 1 0 1 0 2 0 0.823
7 Brian Bogusevic 2011-08-16 HOU CHC W 6-5 1 1 0 0 1 4 0 0.813
8 Brandon Allen 2012-04-26 TBR LAA W 4-3 1 1 0 0 1 2 0 0.805
9 Brooks Conrad 2010-05-20 ATL CIN W 10-9 1 1 0 0 1 4 0 0.805
10 Barry Larkin 2003-05-06 CIN STL W 6-5 1 1 0 0 1 2 0 0.793
Provided by Baseball-Reference.com: View Play Index Tool Used
Generated 6/18/2012.

But wait, there’s more.

Brayan Pena’s not only on the Top 10 Pinch Hit WPA leader board for the last ten seasons. He’s on that leaderboard for the last twenty seasons. That’s right, if we look at all “single” pinch hit plate appearances going all the way back to 1993, we find Pena’s walk-off single against the Brewers at number ten, as ranked by WPA.

Rk Player Date Tm Opp Rslt R H 2B 3B HR RBI BB WPA
1 Mike Lieberthal 1998-06-16 PHI PIT W 8-7 1 1 0 0 1 3 0 0.907
2 Donnie Murphy 2010-07-19 FLA COL W 9-8 1 1 0 0 1 2 0 0.902
3 Bill Hall 2004-04-27 MIL CIN W 9-8 1 1 0 0 1 2 0 0.899
4 B.J. Upton 2007-09-08 TBD TOR W 5-4 1 1 0 0 1 2 0 0.896
5 Jason Giambi 2008-06-05 NYY TOR W 9-8 1 1 0 0 1 2 0 0.895
6 Kirk Gibson 1995-05-26 DET CHW W 8-7 1 1 0 0 1 2 0 0.892
7 Scott Spiezio 2000-07-31 ANA DET W 5-4 1 1 0 0 1 3 0 0.887
8 Jeff Abbott 2000-05-13 CHW MIN W 4-3 1 1 0 0 1 2 0 0.886
9 Rusty Greer 1995-06-02 TEX MIN W 6-5 1 1 0 0 1 2 0 0.844
10 Brayan Pena 2012-06-14 KCR MIL W 4-3 0 1 0 0 0 1 0 0.831
Provided by Baseball-Reference.com: View Play Index Tool Used
Generated 6/18/2012.

For a franchise that hasn’t much to cheer about in the last twenty years, the Royals and their fans can — and should — celebrate Brayan Pena’s game-winning, opposite-field single against the Brewers on June 14, 2012. It was one for the ages.