If Perlozzo yells "Stay," the Phillies will have a runner on third with one out. In 2009, whenever a team was in this situation in an inning, it scored 0.965 of a run on average. That's the equivalent of hanging on to your dollar bill. If Perlozzo yells "Go," one of two things will happen: Rollins will be safe or out. If he's safe, the Phillies get that run and have the bases empty with one out -- which in 2009 produced 0.279 runs on average for a total of 1.279 runs in the two situations. If Rollins is out, there will be no one on base with two outs, which had an average run expectancy of 0.106 runs.
There's a run and an out at stake, both valuable in baseball. How can you tell whether it's a good bet?
Without going into all the algebra, it says Perlozzo needs to be 73.2 percent sure that Rollins will make it before he sends him. So, if third-base coaches leaguewide are playing the game correctly, we should see that about 73 percent of the runners in this situation wind up scoring.
In 2009, there were 97 instances when this sort of situation occurred: no outs, runner on third, fly ball to the outfield. When the runner tried for home, he was safe 96.2 percent of the time (75-for-78). In fact, Perlozzo himself was perfect in 2009: 100 percent of the runners he sent in this situation (and in all sacrifice fly situations) reached home safely.