LOL
Here is what Farrell is dealing with several times a game, every game:
To get a sense of all that goes into the decision, here's a taste of the factors adding branches to a manager's decision tree:
What is the situation? (score, inning, game importance, etc.)
Who is due up for the opponent?
Are there likely to be higher- or lower-leverage situations after this one?
Should I bring in a left-handed or right-handed pitcher?
When might a LOOGY be best deployed?
How many left-handed and right-handed pitchers do I have?
Is the opposing team a good low-ball or high-ball hitting team?
When was the last time each of my relievers threw?
How many days in a row have they thrown?
How many pitches did they throw over their most recent outings?
How do my relievers feel?
Did anyone have difficulty getting loose recently?
Is anyone coming off an injury?
Does any typically take longer to warm up?
Did anyone have poor command while throwing in the bullpen?
What's coming up on the schedule that I should be aware of?
How have my relievers been performing?
Am I going to need multiple relievers this inning?
Does this situation align with someone's role (e.g. setup man, closer)?
If so, will making an exception have motivational or psychological fallout?
That's a lot of things to consider. By no means is it a complete list, but simply a place to start when trying to think like an MLB manager. Keep in mind that not only does the manager need to go through all of those factors and pick the "right" guy, he needs to figure all of those things out far enough in advance for his relievers to properly warm up, far enough in advance, in fact, that he hasn't already blown his desired reliever in a less optimal setting earlier in the game, or even earlier in a series.
From Baseball Prospectus http://www.baseballprospectus.com/article.php?articleid=27403