Hola Joaquín,

En realidad, más que un término específico del béisbol en sí, es un término específico de las apuestas sobre este deporte.

Como verás, un encuentro de este tipo modifica las condiciones de una apuesta, pero no siempre de la misma manera (mi primera idea fue usar el término "nulo", pero no parece ser así, al menos no siempre).

No estoy seguro de qué condiciones específicas que se aplicarán para un "off-pitcher" en un double-header, pero lo llamaría genéricamente "encuentro/partido de/con lanzador modificado", aunque no sé realmente si existe ya otro término ya acuñado.

Espero al menos que el texto te aclare algo:

He encontrado un texto que explica lo que es un "off pitcher":

Listed Pitchers and ‘Off’ Pitchers (Baseball):
Baseball straight bets are accepted in the following ways:

1. "Action": bet team against team, regardless of the starting pitchers.
2. On Specified (Listed) Pitcher: wager on one specific starting pitcher, regardless of the other starting pitcher. Specified pitcher must start or your wager is "no action" and amount wagered is refunded.
3. Against Specified (Listed) Pitcher: wager against one specific starting pitcher, regardless of the other starting pitcher. If pitcher specified against doesn’t start then wager is no action.
4. List Both Pitchers: wager specifies both starting pitchers. If either or both do not start, wager is no action.

Note: each team’s starting pitcher is defined for wagering purposes as the pitcher that throws each team’s first pitch.

Example: RED SOX J BECKETT +120
YANKEES R CLEMENS -130

In this example, there are 4 ways to bet the YANKEES. You could take Yankees “Action” meaning you want the YANKEES -130 over RED SOX regardless of starting pitchers for either team. You could also bet Clemens -130 versus RED SOX , YANKEES -130 versus Beckett, or Clemens -130 versus Beckett. The same 4 options apply to taking the underdog, RED SOX (J Beckett).

An "off" pitcher occurs when either starting pitcher is replaced from the time odds are posted until the start of the game. In the event of an off pitcher, money odds on straight wagers may be adjusted.

In the event of an off pitcher has replaced a specified pitcher, the bet is deemed no action. In the event that “Action” has been taken or the one specified pitcher still remains live, then wagers will be computed at the opening price established with the new starting pitchers.

Using the previous example, if Petitte starts in place of Clemens:
1. "Action": You still have YANKEES versus RED SOX but at adjusted price with Petitte starting versus Beckett.
2. Clemens versus RED SOX: Bet would be no action as Clemens is listed and no longer starting. Wager is refunded.
3. YANKEES versus Beckett: Still have YANKEES at adjusted price with Petitte pitching.
4. List Pitchers: Bet is no action as one of the there is an off pitcher for one of the original starting pitchers (Clemens). Wager is refunded.

Using the same example, if Clemens remains starter and Schilling starts in place of Beckett:
1. "Action": You still have YANKEES versus RED SOX but at adjusted price with Clemens starting versus Schilling.
2. Clemens versus RED SOX: Still have Clemens at adjusted price with Schilling pitching.
3. YANKEES versus Beckett: Bet would be considered no action as Beckett is listed and no longer starting. Wager is refunded.
4. List Pitchers: Bet is no action as one of the there is an off pitcher for one of the original starting pitchers (Beckett). Wager is refunded.

IMPORTANT: Both starting pitchers are automatically specified on baseball totals and run line wagers. If either listed pitcher does not start, totals and run lines are deemed no action. So in our example, if either Clemens or Beckett did not start, any run lines or total bets would be considered no action.

http://www.fantasysportsbook.com/odds.aspx#Listed

Suerte y :O)

Álvaro