Expected Run Value. An acronym for Expected Run Value, ERV is the unit of value in the PROTRADE baseball system. It refers to the change in the number of runs that a team is expected to score based on an action. An inning begins with an expected run value of approximately .5 runs. If, for example, the first walks, the expected run value is now about .9 runs. The difference between the state after the at-bat and before it (.9-.5 = .4) is the ERV on the play. The ERV is allocated among the participants (in this case, the batter and pitcher). Also, see "Value allocation."