Player teleporting

use the procedure block in the entity section "execute command / [your command] in the name of event/target entity" and put the command "teleport @s" and then then put the x, y, and z values you need to appear behind the entity. You can get the x, y, and z by using the block "x position of event/target entity" but switch the "event/target entity" with "source entity" and ajust the value by using math block until you get a result you are happy with.