פירוש על עבודה זרה 119:3

If the non-Jew is holding a barrel of wine and pouring the wine into a cask held by the Jew, then the wine is prohibited because it is coming out from the force of the non-Jews.

If the Jew is pouring, the wine is permitted, because the non-Jew is just acting passively. However, if the non-Jew tilts the cask then the wine has moved due to his power and it is prohibited.