The Book tells us
"The old-school book says the rest of the lineup should be written in based on decreasing talent. Hitting ninth is an insult. The Book basically agrees, with a caveat. Stolen bases are most valuable ahead of high-contact singles hitters, who are more likely to hit at the bottom of the lineup. So a base-stealing threat who doesn’t deserve a spot higher in the lineup is optimized in the #6 hole, followed by the singles hitters."
So with Francisco Cervelli projected to be the Pirates sixth best hitter, .320 wOBA. But he doesn’t have the stolen base threat that Josh Harrison possesses. Harrison has swiped 18, 10, and 19 the last three years. He will likely be in the 15-20 range again in 2017.
Cervelli is a high contact hitter, posting contact rates of 75.7, 82.1, and 80.4 percent since 2014. Over the last three years, the league average (nonpitcher) rates are 79.5, 79.1, and 78.4 percent. Cervelli also has a career contact rate of 82 percent.
Cervelli is also a singles hitter, posting ISO’s of .106 and .058 the last two seasons. The last two seasons, Cervelli singled in 22 percent of his at-bats and 19 percent of his plate appearances. League average those two years were 17 percent and 15 percent respectively.
Cervelli’s projected ISO of .096, once again a high-contact singles hitter. Harrison’s stolen base threat has him sixth, which leaves Cervelli seventh.