Most pitchers don't have the same power when pitching from the stretch position as they do from the wind-up.
Often times, pitchers are more careful when runners on base, particularly when the runners are in scoring position. Careful is not necessarily an effective way to pitch. Careful pitchers work the strike zone more frequently than trying to get batters to chase pitches.
The point here is that it is not a surprise that teams hit better with runners on base than when the bases are empty.
Take a look at the AL teams
As you scan over the icons you will see three teams where the norm is reversed: the Texas Rangers, the top hitting team with the bases empty in the AL, the Angels, and the Yankees.
The Tigers are the top hitting team with runners on base followed by the Red Sox.
The Tigers are hitting 33 points higher with runners on base.
The Red Sox are hitting 30 points higher with runners on base.
The Indians are hitting 25 points higher with runners on base.
But the honor for the greatest differential belongs to the Tampa Bay Rays who are 12th in the league hitting just .238 with the sacks empty and are fourth in the league in batting with runners on at .285, a 47 point differential.
Let's look at the NL
Six teams, the Braves, Cubs, Reds, Dodgers, Brewers, and Phillies are all hitting better with the sacks empty. Damn you, hitting pitchers!
In addition, the differential though is also minimal with the Pirates (one point), Diamondbacks (two points), and Giants (four points).
The Rockies are hitting 47 points better with runners on base but the big story is the astounding differential for the team with the best record in baseball: the St. Louis Cardinals who are hitting 93 points better with runners on base.
The Cards are ninth in the league in hitting with the bases empty, .233, but lead the world in hitting with runners on base hitting .326.
Just in case you were wondering why the Cards are 39-21, you might follow how well these guys hit with runners on base: