I don't know, but you may be thinking of w/risp, which just means "with runners in scoring position." Usually, you'll talk about a player's AVG or SLG split for w/risp or vs. lefthanded pitchers. That information can be looked up at ESPN, Yahoo, or MLB.com—for example, Albert Pujols' split page is here. There are splits for all sorts of stuff, of varying value, including by count, with runners at certain bases and with so many outs, or even against a certain style of pitcher, like a power pitcher or a finesse pitcher, as classified by a metric that counts traditional things like walks, strikeouts, and flyballs. Some splits are more useful than others: w/risp probably is; vs. left definitely is.

You break down every game in the retrosheet database by game situation—such and such inning, so many outs, runners on certain bases, runs on the board. Then you figure out the percentage that each game situation results in the team winning. This gives you a relatively uninteresting table of percentages. For example, a situation where you have men on first and second in the bottom of the ninth with two outs, your chance of winning is about 90%. But then when Albert Pujols hit the home run off Brad Lidge last NLCS game 5, the percentage of the time that the Astros win the game in the situation they then found themselves in had dropped to something around 20%. Those changes in winning percentage by a player changing the game situation is the WPA, the winning percentage added. In that case, El Hombre added about -70 percentage points to Houston's probability of winning the game. I know that by looking at the fangraphs.com page for that game. Obviously, building a WP database and producing graphs of it is enough work that the people maintaining that site are able to sell advertising to support their efforts. Too much work for most of us to do ourselves...