Originally Posted by Sea Ray
I don't know what win probability is but I imagine it's not good when only 6 of your players are in the + category
In its most simple form, you take the win probabilty before a certain AB and after the result and attribute the difference to the batter (and pitcher).
At the end of the season the sum of the individual players WPA will equal the team's games over/under .500. (divided by 2).
It is a loose measure of "clutch".